Since Bryan Caplan has been a sort of godfather/patron figure for this blog from the beginning, I thought it might be of interest to readers to outline a few points where I dissent from him. In general, I admire Caplan as a writer whose lucidity, range, and right-mindedness on most issues has few peers today. That’s not just one libertarian admiring another. Caplan’s writings on family, public choice, and free will, though not inconsistent with libertarianism, are largely independent of it, and here too I admire and largely agree.

I also like Caplan’s choice of which libertarian causes to champion and to neglect, which to carry to extremes, and which to be compromising and squishy about. Mainstream libertarians are wrong (in my view) about gay marriage and abortion, and they overvalue gun rights. Caplan doesn’t promote those causes much. Caplan is also right not to champion Austrian monetary austerity and the gold standard, as some libertarians do. Immigration, meanwhile, is the issue on which libertarians most dominate the moral high ground, and on which extreme libertarians are more correct than the moderates and compromisers, and here Caplan is most vocal and purist.

It feels odd to call Caplan “wise,” since he always somehow has the air of a smart-alek teenage kid with pimples and a baseball cap. (I think it’s because he engages in intellectual debate with in the same spirit of light-hearted, competitive fun that kids play baseball.) But I’ll do it anyway. You don’t get so many issue positions right on the basis of analytical cleverness alone. It takes wisdom. Caplan’s pacifism is the part of his intellectual agenda I have the least sympathy with, but even here, his frank naivete is calculated to be a useful provocation to gutsy, nuanced thinkers with more of the truth here than Caplan has, to explain themselves better.

Nonetheless, the deep philosophical differences between myself and Bryan Caplan are really rather large. Let me start with the topic of “cosmopolitan tolerance.” In a recent post, Caplan called cosmopolitan tolerance “the sweet spot of freedom.” He argued that free societies are best served when people don’t feel disgust or hatred for their fellow human beings (obviously, since that would make them want to oppress and persecute them), nor indifference, nor love, but moderate benevolence. Indifference is better, but freedom, after all, benefits one’s neighbor as well as oneself, so moderate benevolence towards others is likely to strengthen a person’s commitment to the values of a free society. But why not love? Because

default emotions like love and devotion are also inimical to human freedom.  If you love every stranger like your own child, the idea of respecting their freedom to make their own mistakes is hard to stomach.  You’ll want to give strangers what they need, regardless of what they want.  This yearning makes both paternalism and the welfare state quite enticing.

That’s a very interesting argument, but I would take the Christian view that the ethical ideal is to love one’s neighbor as oneself, where one’s neighbor– as the parable of the Good Samaritan (Luke 10:25-37) illustrates– means anyone you happen to come in contact with, who is in evident need. Is that “inimical to freedom?” Surely, it’s evident that the Good Samaritan’s benevolence is not inimical to the freedom of the robbed man. He wasn’t helped against his will. Nor did the Good Samaritan aid the wounded man with other people’s tax dollars, but out of his own generosity. But mightn’t the Good Samaritan’s general attitude of generosity towards strangers induce him to support paternalism and the welfare state? I doubt it.

First, an immediate response to an unmistakable need is quite a different matter from a programmatic purpose of bettering the human condition, and I don’t think the psychological motives of the two are very similar. Second, the Good Samaritan’s attitude is consistent with epistemic modesty and respect for the rights of others, and I believe it is those traits that a judicious anti-paternalist should seek to encourage. Don’t seek to restrain people’s benevolence for their fellows. Instead, stress the need to respect the rights of others, to let them live their own stories, and have their own adventures. Let us remember that man does not live by bread alone, that adversity is often a good teacher, and that kindness, clumsily and patronizingly bestowed, can corrupt and demoralize a person. Let us remember Gandhi’s critique of philanthropy, and his saying that

“Service which is rendered without joy helps neither the servant nor the served. But all other pleasures and possessions pale into nothingness before service which is rendered in a spirit of joy.”

Exactly. Or as G.K. Chesterton put it, the philanthropist differs from the lover of humanity because he may be said to love anthropoids, whereas the lover of humanity loves men. Certainly, we should restrain out benevolent impulses when they tempt us to violate the demands of prudence or justice. Certainly, we should make sure that our service is rendered joyfully, and with a view to the real flourishing of our fellows, and not simply because we want to remove their suffering as an eyesore. We should never forget that it is infinitely more important for our fellows to be virtuous, than to be well-fed, and that it can be an injury to a man to encourage his vices by giving him help that he does not deserve and is sure to abuse. But our attitude towards our fellows ought to be love, and the more of it there is, the better.

If anything, I think people support both the welfare state and immigration restrictions because they don’t want to be Good Samaritans. They don’t want to see unmistakable needs and feel they ought to help with their own resources, so they demand that the government mitigate poverty domestically, and they erect the border as a blindfold. The border is their way of walking to the other side of the road and pretending not to see, like the priest and the Levite in the parable. I sometimes joke that “I support the abolition of private property rights, by moral suasion.” That is, by all means, let money be redistributed from rich to poor, but let it be voluntarily given, not taken by the government. By all means, let goods be shared and held in common, but let that be because their owners share them freely and with a good will, not because they are taken from the owners by force.

Caplan has championed “cosmopolitan tolerance” as one of the advantages of open borders, arguing that “immigrants are good for cosmopolitan tolerance,” and, assuming this point is accepted, adds:

I can’t even figure out what social disasters nativists will try to pin on cosmopolitan tolerance.

So I ask them: What country has ever suffered from cosmopolitan tolerance run amok?  From focusing on people’s common humanity rather than superficial differences?  From judging people on their merits instead of their origins?  From living and letting live?

This is an interesting challenge. The word “cosmopolitan” comes from the Greek cosmos=world and polis=city, but in the sense of the city-states of ancient Greece, so “country” would be almost as good a translation. A cosmopolitan, then, is someone who feels that “the world is my city.” But is it possible to feel that way, without a certain loss of the fond attachment to hearth and home, which is also one of life’s pleasures? A sturdy peasant for whom every stone of his native village is sacred, and whose enjoyment of it is proportional to his love, is not very cosmopolitan, yet may have a greater share of wholesome and fruitful happiness than most urbane citizens of the world. If anything, I’m inclined to think that being cosmopolitan is correlated with being discontented, restless, and easily bored. Not that cosmopolitanism is a vice. It’s probably a minor virtue, though a costly one to acquire, and hard to separate from associated vices like superciliousness and indifference. Rootedness is also a virtue, and a more important one. It’s good to love one’s own home, and also to have such broad exposure to the common heritage of mankind that one really feels the whole world is one’s city. But to combine these opposite virtues is a rare attainment, and if cosmopolitanism comes at the cost of not feeling at home anywhere, it is too dearly bought.

As for tolerance, it is subject to this paradox: that a society cannot be tolerant without being intolerant of intolerance. To see why, imagine a society where 95% of the population is highly tolerant both of homosexuals, and of violence against homosexuals. Gay people in this society can take pleasure in the knowledge that the vast majority of their fellows look upon their lifestyles with perfect equanimity, and do not judge or condemn them in the least. Alas, the tolerant majority looks with the same equanimity on a small minority of self-appointed divine avengers of sodomy and perversion. When such thugs attack a homosexual in the street, the crowds will not sympathize, but will reflect that, after all, who are they to judge? How can they condemn the sincere expression of someone else’s ethical beliefs? Clearly such tolerance is hardly worth having. Gay people would probably prefer to live in a society which is moderately intolerant, as a matter of morals though not in law, of homosexual behavior, but is also uncompromisingly and aggressively intolerant of violence against homosexuals.

American society today is intolerant of aggression; of racism; of proposals for ethnic cleansing; of the Inquisition; of fascism and communism; of polygamy. It harbors a propensity to lash out against “sexism,” even though this word does not, as far as I can tell, refer to any actual coherent concept, but means whatever a person who chooses to be offended wants it to mean at a given moment. Some parts of American society are becoming intolerant of the idea that marriage necessarily refers to an attachment between a man and a woman. I regard some of these intolerances as bad, but to regard intolerance in general as bad doesn’t fundamentally make sense. You can’t really even make a coherent distinction between moral progress and intolerance of the moral evils that moral progress overcomes. As an open borders advocate, I don’t want to make America more tolerant, but in a sense, less so. I want people to be fervently intolerant of the use of force to exclude or remove immigrants.

And that does not apply only to moral evils. A useful reductio ad absurdum of the idea of tolerance is to imagine a tolerant classroom, in which the teacher scrupulously avoids imposing her views, instead tolerating any opinion that might be expressed. She might humbly suggest that the derivative of sin x is cos x, or that the Declaration of Independence was signed in 1776, but far be it from her to repress or punish a student who, on an exam, expresses a different opinion. The lesson here is that one can’t pursue excellence without being intolerant of mediocrity, and this applies at the societal as well as the individual level.

Historically, the societies most notable for the successful pursuit of excellence fulfilled very imperfectly the desideratum of cosmopolitan tolerance. Victorian Europe, the wellspring of such dazzling progress in science and exploration and economic productivity and literature as the world had never before seen, was notoriously disdainful of non-European peoples. Classical Greece, birthplace of philosophy and democracy and geometry and the proto-scientific study of nature, classified the rest of mankind contemptuously as “barbarians” and was sometimes even ready to regard them all as natural slaves to the free and enlightened Hellenes. Western Europe in the High Middle Ages, birthplace of scholastic philosophy and natural science and the university and the Gothic cathedral and great modern nations like England, France, and Spain, as well of the common law and proto-democratic representative institutions of England that in due course became the basis for modern political liberty, was admirably international as far as Western Christians were concerned, but regarded everything outside “Christendom” as more or less evil and benighted.

By contrast, in response to Caplan’s challenge to find a society of excessive cosmopolitan tolerance, I would name the Roman Empire. There, the many nations of the ancient Mediterranean met and mingled, promiscuously exchanging myths and gods and cults and light philosophical ideas and goods and slaves. They called it the Pax Romana, but it was a time when Roman republican liberty surrendered to the tyranny of the Caesars, and the intellect atrophied and descended gradually into mediocrity. Of course, the late Roman Empire wasn’t entirely tolerant as we mean the word. Thousands of Christian martyrs died gruesome deaths merely for refusing to engage in the nominal emperor-worship which the rest of the population indifferently and ironically engaged in. But principled religious toleration hadn’t been invented yet. The Roman Empire acted to defend the civic unity expressed in the imperial cult, but its general attitude was one of tolerance, of live and let live. It tolerated a labyrinth of religions and cults, it tolerated prostitution, it tolerated social practices like slavery and infanticide. And it gradually ran down, degenerated, and fell apart.

The Christian Church, which took over at the last minute and carried the torch of the classical Mediterranean civilization through the Dark Ages, is often blamed for its intolerance. That this is a somewhat unfair charge is easily seen in the fact that pagans fed Christians to the lions, not vice versa. But Christian emperors did eventually close pagan temples, prohibit pagan sacrifices, remove the pagan Altar of Victory from the Senate, and suppress the ancient Olympic Games. All these changes were perceived by pagans as attacks on their ancient rites, and rights, but to charge the Christians with persecution in the modern sense is complicated by the statist nature of paganism. Thus, as pagan temples had generally been built, maintained, and operated to a large extent at public expense, their closure could be seen as a measure to improve the public finances by cutting spending on things the majority no longer wanted much. Morally, though, the charge of intolerance is apt. Christian churches were intolerant of infanticide, crucifixion, suicide (which had sometimes been ordered by the state), and sexual exploitation of slaves, and the process of moral improvement that it initiated led on to the near disappearance of slavery from medieval Europe. It’s a good thing the Christian churches dispelled the corrupt and enervated cosmopolitan tolerance of the Roman Empire, and replaced it with a moral fervor to better the human condition.

One more critique of Bryan Caplan probably deserves to be the topic of another post, but I’ll add it here briefly, because I might never get around to writing that post. In his book Myth of the Rational Voter, Caplan writes as an unabashed epistemic elitist. His thesis is that democracy is vitiated by the “rational irrationality” of voters, who indulge their biases (the make-work bias, the anti-market bias, the pessimistic bias, and the anti-foreign bias) because their vote won’t affect election outcomes anyway, so they have no incentive to make sensible choices at the ballot box, as opposed of doing whatever feels good. That voters have these particular biases, Caplan establishes by looking at survey data and showing how the views of ordinary people on the economy deviate from those of economists, who presumably know better. His assumption here is that experts know best, and that voters’ disagreements with the experts are evidence of voters’ (not experts’) mistakes.

But lately, Caplan seems more and more to position himself as a champion of common sense. He extols philosopher Michael Huemer for building a political philosophy on “common-sense morality,” and makes a “common sense case for pacifism,” which strikes me as merely evasive since it isn’t utilitarian, but rather seems to take a type of natural rights line that would lead to something close to Tolstoyan pacifist-anarchism, which however he arbitrarily stops short of, calling it “too broad.” This common-sense philosophy seems to be the platform from which Caplan attacks theories favored among the elite, such as John Rawls’ veil of ignorance. Now, if Caplan had simply said that sometimes the common sense of ordinary people is right, against the experts, and sometimes the experts are right, against the common-sense of ordinary people, there would be no inconsistency. We’d presume that neither source of knowledge is epistemically foundational in itself, and look for other sources that are. But as general epistemic principles, “trust the experts” and “rely on common sense” are a bit inconsistent. If they are to think clearly and follow the evidence where it leads, experts need to be able to reject common-sense opinions sometimes. Conversely, if a maverick intellectual like Caplan wants to reject this or that elite consensus with an appeal to common sense, isn’t he obliged to defer to the opinion of the common man on other questions, too, including questions where common sense doesn’t support him?

This strikes me as a fatal flaw in the Caplan-Huemer project to found an anarcho-capitalist political philosophy on common-sense morality. Yes, the non-aggression principle has a basis in common sense, but so do the notions that governments make laws and citizens should obey them. If one’s epistemic starting place is that common sense is reliable, one has surrendered ex ante the option of rejecting things like governments or migration restrictions that everyone nowadays takes for granted. I would advocate a more critical approach to common sense, distinguishing intuitions about natural rights, which are an indispensable source of ethical insight, from customs and tradition, which are a fallible but very valuable repository of lessons mankind has learned, and to which great but not unlimited deference is due, from self-serving prejudices, rationalizations, and bad habits, which can pass easily and perhaps validly for common sense, yet which need to be smoked out and rejected. I think respect for common sense is an amiable, humble, and often useful habit for a thinker to have. It reminds a thinker of the complexity of the world. But one can’t articulate anything clearly, or follow any sophisticated chain of logic, or conduct an experiment, without departing somewhat from common sense, and entering the rarefied, elite world of theory and expertise.

The draft of my paper “The Global Economic Impact of Open Borders” already feels a bit obsolete after some great real-time peer review and the rethinking it has been provoking me to do. Sometime soon (I hope) I’ll do a rewrite, but it’s already reshaped my thinking about what a world of open borders is likely to look like. I thought a Q&A format might be a good way to explain my methods, highlight some key predictions, and give voice to some of the skepticism readers are likely to feel, responding to it with a mix of rebuttal and concession. “Q” represents my impression of an intrigued, but sometimes confused or skeptical, reader. “A” is me in my role as author of the paper.

Q: Does your paper confirm the well-known claim that open borders would “double world GDP?”

A: Basically, yes. “Double world GDP” was always a kind of very rough midpoint of disparate projections. I present two scenarios, with Scenario 1 predicting an 80% increase in world GDP, and Scenario 2 predicting a 69% increase in world GDP. That’s less than doubling, but it’s in the ballpark.

Q: How many people would migrate?

A: Very many. Scenario 1 predicts well over 5 billion, Scenario 2, a little over 3 billion. This is one of the respects in which I think Scenario 2 is more realistic. By this account, international mobility under open borders would actually be similar to current levels of mobility among US states. That might sound odd, since, policy aside, the cultural and linguistic barriers to international migration are obviously much larger than for migration among US states. But the economic incentives for international migration are also larger. Wages and the general level of economic development differ far more among nations than across US states.

Q: Would open borders end world poverty?

A: That’s a little complicated because “poverty” is not well-defined. Have we ended poverty in the USA? Probably almost any American would say no. A development economist might be tempted to say yes, because even Americans below the “poverty line” tend to have plenty to eat, electricity, shoes, indoor plumbing, and all sorts of other things that would be luxuries in sub-Saharan Africa. Granted, people in homeless shelters may not have even that, but (a) they’re a tiny proportion of the population, and (b) since other factors like mental illness or substance abuse, or mere lifestyle choice, often account for homelessness, it’s not clear that “poverty” is the right diagnosis of the problem. Still, it would be too odd to claim that poverty has been eliminated in rich countries, and the lesson one learns in being forced to concede that is that poverty isn’t just a matter of not having enough money or material resources. It’s partly a matter of relative living standards, of social status, of character and mentality.So, I would not really want to claim that open borders would end poverty. I would almost want to say it would eliminate “world poverty” but not “poverty” because when we say “world poverty” we mean something more extreme than when we say “poverty”… but that seems like verbal hair-splitting. Let’s say that open borders seems likely to eliminate, or at least to render rare to the point of negligible, the kind of extreme poverty that development economists usually have in mind when they talk about poverty, e.g., in Paul Collier’s book The Bottom Billion. Under my “Scenario 2,” the living standards of unskilled workers would converge to 44% of the current US level. If by “poverty” we mean $1/day or $2/day, that’s pretty much the end of world poverty.

Q: What’s the deal with “sigma?” Does the model really assume that unskilled workers have to be paid 1,000 times more to live in a big metropolis, compared to a small village? Is that plausible?

Sometimes economists have to use unrealistic assumptions to make a model work. Milton Friedman argued that the value of an economic theory depends on the accuracy of its predictions and, in effect, that it doesn’t matter how unrealistic one’s assumptions are. Someone pointed out (I can’t find the citation) that by that standard, “giants paint the sky blue every morning” is a valid theory, because its prediction– that the sky turns blue in the morning– is true, and the falsity of the assumption that giants are painting it is irrelevant. So, Friedman can’t be quite right… yet the idea of “market equilibrium” does seem to help economists understand the world, even if it’s never quite a true statement to say “this market is in equilibrium.”

At present, I need the unrealistic assumption of a high “sigma” in order to avoid imputing highly compressed distributions of local TFP to settlements in rich countries. Highly compressed distributions of local TFP within countries, mean small overlaps of local TFP distributions across countries, leading to extremely high total migration under open borders. By making “sigma” more realistic, I would make the model’s other predictions wildly unrealistic. Doesn’t that show that there’s something wrong with the model? Well, yes… but, what’s the alternative? Build a better model? Easier said than done. Just guess, without a model. No thanks, I prefer a flawed model (used with good judgment) to mere verbal hand-waving.

That said, I’m working on changes that will hopefully eliminate the need for an implausibly high “sigma.” Currently, the model has two extreme assumptions about how population density affects the cost of living. On the one hand, the elasticity of the raw wage with respect to settlement size (i.e., sigma) is 0.6. On the other hand, the elasticity of the human capital premium with respect to settlement size is zero. These assumptions are unrealistic in opposite directions, and may even cancel each other out in some respects, but it would be better if both the raw wage and the human capital premium were higher in cities. The elasticity of the human capital premium with respect to settlement size probably should be lower than the elasticity of the raw wage, since a lot of what cities have to offer, over and above what the countryside can, is of a luxury character (e.g., fancy restaurants) and/or more enjoyable to people with high human capital (e.g., museums). But it makes sense that lawyers and doctors should want to spend some of their extra earnings on backyards, not just on manufactured goods or foreign vacations or fine wines.

The question is: will the math still work? It’s almost impossible for laymen to understand this aspect of the alchemy of economic modeling. A non-economist, or even a well-trained economist, will suggest a plausible modification, seemingly simple and realistic, and the modeler stubbornly refuses to incorporate it. Little does the friendly critic know that his tweak breaks the solvability of the model. The difference between being able to solve for equilibrium, and not being able to, is like the difference between gliding along a bike path and hacking one’s way through the forest. Solvable means you can derive nice elasticities, and see how your variables and parameters are affecting your results. Not solvable means exorbitant computations to check any tweak of a parameter or a variable, and causation is still opaque.

But, I’ve started to work through this, and I think the math will work. So, in the next version of this paper, I may be able to dispense with the need for a high “sigma,” and the weird assumption about unskilled workers earning 1,000 times more in the big city than in the village. If not, I’m not above publishing a model that has a few giants painting the sky blue, if it enables me to perform mighty feats of plausible extrapolation.

Q: What’s the deal with these “new settler societies?” Are they just data artifacts?

A: “Scenario 1” makes some odd predictions to which I give the appealing name “new settler societies.” Thus, East Timor ends up with 478 million people (from just over 1 million), Botswana with 212 million (from a little over 2 million), and Swaziland with 138 million (from a little over 1 million). Under “Scenario 2,” the phenomenon is much less dramatic, but it’s still there. East Timor’s population soars to 43 million, Botswana’s to 36 million, and Swaziland’s to 35 million. I classify Qatar differently, but it would also see a surge in population, to 391 million.

Doubtless, these results are partly artifactual, and specifically, they reflect anomalously high “TFP” that is really just natural resource extraction, not extensible over a greatly increased population. I need better ways to quantify natural resource extraction and subtract it from GDP. (Currently, I have patchy data about oil exports, which I deduct from GDP, but I need a more refined and comprehensive approach.) It’s possible that if I had better data on non-natural-resource-extraction GDP, the “new settler societies” would disappear. Then again, a lot of resource-rich places didn’t show anomalously high TFP.My tentative guess is that the specific “new settler societies” that show up in my predictions are largely artifactual, but that there would be such a phenomenon as new settler societies under open borders. In certain places, a happy combination of natural and political circumstances would give rise to a fashionable migrant mecca, and a cosmopolitan settler community, self-selected to prefer the kind of society chance and circumstance had thrown up, would reinforce it. A virtuous cycle would ensue, and soon, some spot hardly anyone has heard of would be an admired and thriving city, with suburbs spreading out and skyscrapers surging up. And without claiming the site is specially probable, I see no harm in imagining the place to be East Timor, with lots of coastline, a tropical climate, and mountains. Why shouldn’t a flood of Chinese and Indians settle there, and found a string of Singapores?

Q: And meanwhile, there would be quite a few “ghost nations?” Sounds spooky.

Yes, it sort of does. This is one of the predictions of Scenario 1 that goes away in Scenario 2. Still, it has a certain logic to it. Why would anyone live in a place like Zimbabwe, Afghanistan, the Democratic Republic of the Congo, or Burma, unless they had to? According to Scenario 1, almost no one would. There would be a nearly universal exodus, leaving behind only a few half-mad beggars wandering among the deserted shantytowns.

According to Scenario 2, there are no ghost nations. The worst-off places would see a major exodus, but at some point they would be “rescued” by their diasporas. I think this is more likely. Large diasporas could undermine bad regimes and foster better ones. Some would return with skills and/or savings, start businesses, run for office, teach school. Migration would plug these countries in to world civilization, and they would change.

Q: But anyway, wouldn’t the governments of these countries restrict emigration, if they were on their way to becoming ghost nations?

Maybe, but the game is to predict what would happen if migration restrictions were abolished. So that’s ruled out by assumption.

Q: What’s the deal with “Scenario 1” and “Scenario 2?”

Scenario 1 applies the model in a straightforward and literal way. The result is that the tail of TFP ends up wagging the dog of global migration. TFP, or “total factor productivity,” is a kind of residual or “pure place premium.” TFP is the differences in GDP per capita that can’t be explained by other systematically observable and quantifiable variables. Now, I actually argue that “factor endowments” can do most of the work in explaining GDP per capita, leaving a relatively small explanatory burden for TFP. I see the wealth of nations as arising mostly from (a) large international differences in average human capital and (b) substantial country risk premia affecting the risk of investment capital, with TFP varying across countries much less than average human capital. Still, under open borders, because everything else is mobile, a little bit of TFP can move a lot of people. Hence the new settler societies mentioned above.

For Scenario 2, I (a) assume that open borders promotes human capital development, with the average native of each country closing 20% of the human capital gap with the US; (b) assume that open borders facilitates international capital flows, cutting in half the risk premia faced by many countries; and (c) adjust TFP downward in receiving countries, so that it shifts in the direction of the TFP of source countries, and adjust TFP upward in sending countries, so that it shifts in the direction of the destination countries. Migrants affect TFP both where they come from, and where they go to, albeit with one-fifth the weight of non-migrants in each case, reflecting the greater influence on institutions of those who stay put. All these modifications are very plausible qualitatively, but theory and evidence don’t pin down how they should be quantitatively implemented. Still, for the moment, Scenario 2 represents my “best guess” about what a world with open borders would “really” look like, partly just because the TFP adjustment mechanism reduces the probably distorting effect of apparent high TFP outliers.

I could generate many more of these “scenarios.”  Scenario 1 is to some extent unique, representing “the” result of global market clearing in the labor market, albeit I had some discretion in how to describe the status quo. But for Scenario 2, I had plenty of room to choose the rules differently. In future drafts, I plan to have more “robustness checks” showing how results depend on how some of these discretionary elements are chosen.

Q: Would rich countries by “swamped” by immigrants under open borders?

What do you mean by “swamped?” In Scenario 2, the population of the West (the EU and the Anglosphere) rises from 872 million to over 3 billion. But assimilation would still mostly prevail, at least as far as TFP indicates. Revolutionary English stock a small proportion of the current US population? If the answer is “no, because those immigrants assimilated and didn’t fundamentally alter American society,” then that answer may apply to open borders, too. There isn’t a formal theory of institutions undergirding these results, however, and if you think 3 billion people in the West would lead to complete societal collapse, this paper doesn’t refute that, it just starts with more optimistic assumptions.

I don’t find predictions of 3 billion people living in the West either surprising or alarming. Life is good here. Why shouldn’t almost half the human race want to come? Admittedly, international polls show much lower demand for migration than my model, or, say, John Kennan’s, predict. But that’s just diaspora dynamics. Migration would snowball as early migrants wrote home that the grass really was greener on the other side.

Q: Scenario 2 predicts huge gains in labor income for people in many poor countries? How exactly would that happen?

Open borders would enrich the world’s poorest in several different ways. First, many would move to more productive places. Second, open borders would increase both the incentive and the opportunity for people from poor countries to acquire human capital. Since unskilled workers are far more likely than skilled ones to be stuck in unproductive places under the status quo, open borders would increase the effective global supply of raw labor, relative to the effective supply of human capital. Human capital would become relatively scarcer and see its marginal product rise, giving people an incentive to study. At the same time, higher wages would give poor people more money to invest in their children’s education. And the experience of migration itself– permanent or temporary– would broaden the horizons of many and make them smarter and more modern. And people would get access to better schools in the West. Third, the poorest countries would benefit from having large diasporas abroad, becoming acquainted with better ways of doing things practiced in the rich world. Fourth, remittances from abroad would finance capital formation. Fifth, in some countries it would be important that emigration would raise the per capita value of extractible natural resources. People in the world’s most benighted countries would mostly improve their lot in life by moving abroad. In less desperate cases, such as India and China, around half the population would emigrate, but life would improve a lot for those who stayed behind, as well as for emigrants.

Q: Would Americans really see their incomes fall by 10% under open borders? Why?

Well, real estate would appreciate in value dramatically, so homeowners would see their net worth rise, and maybe their dollar incomes, too, if they went into business as landlords. There would also be a lot more capital in the world, so to the extent that Americans own a substantial share of that, that might also offset a drop in labor incomes. Finally, the US government would enjoy a much larger tax base, so depending on what it did with that, it might contribute something to natives’ disposable income through transfers and/or tax cuts. Also, I’ve left out of account the effect of open borders on technological change, but there are all sorts of reasons to expect open borders to accelerate that, which would bend all the model’s predictions in an appealing direction.

But yes, under Scenario 2, the average labor income of US natives would fall by 10%. And this applies across the human capital spectrum. Unskilled workers would see their living standards (not money wages though) fall to 44% of the current level. But, surprisingly, the human capital premium would fall, too, because the US would be such a magnet for human capital that average human capital would rise in the US. If the only effect of open borders were to increase population while keeping average human capital the same, money incomes would stay the same, though living standards would fall somewhat due to congestion disutilities. What causes a loss of labor income for Americans is that TFP falls under Scenario 2.

Q: How does the spatial model here relate to your OB post about “The Great Land Value Windfall from Open Borders?”

It is somewhat more pessimistic. In that post, I drew two land supply curves, one for existing urban land, one for new urban land. I treated the supply of existing urban land as perfectly inelastic, and the supply of new urban land as perfectly elastic. I treated these as separate markets, on the ground that what one is really paying for in urban land is precisely proximity to other people and centrality of location, so as urban centers grow, new urban land developed at the edges will have the same value as urban land at the edges previously had, but previously developed land closer to the city center will appreciate as the city population grows. In that model, there are no congestion disutilities, and no inherent scarcity of land as such.

In “The Global Economic Impact of Open Borders,” a scarcity of good city sites is a fundamental and important feature of the world. Consequently, mass immigration to the USA would reduce the living standards afforded by a given money income, due to congestion disutilities. In “The Great Land Value Windfall from Open Borders,” mass immigration would not reduce the living standard afforded by a given money income, because newly developed urban land at the margins of cities would be just as good as the formerly marginal land was. The difference between these models is not really accounted for by any change in my views of how the world works. It is simply that different assumptions proved analytically convenient for different purposes.

Q: This model pertains to universal open borders, right? What if open borders were implemented by just one country, say, the USA?

Yes, this model is for universal open borders. I don’t know what would happen if just the USA did it. I’d need to make fundamental changes to the model to answer that question.

Q: What about DRITI?

The paper contains no estimates of how much revenue could be raised by migration taxes, or how a world of open borders would change if governments sought to hold natives harmless through tax-and-transfer schemes.

Q: Do you think this paper should persuade policymakers to adopt open borders policies?

Yes and no. Yes, I think that if my predictions are right, or in the ballpark of right, they would be a very strong reason for benevolent policymakers to open the world’s borders to migration. But no, I of course don’t think it would be sensible for any policymaker to adopt such a radical policy on the basis of such tentative and speculative predictions as my paper contains.

Q: Why is there no literature review, no bibliography, and few citations in the paper?

A: Because it’s just a draft. I like to have a good idea where I stand before I really plow into what others have said. Sometimes you don’t even know what’s relevant until you’ve done a lot of your own exploration. And compiling bibliographies is tedious work. But I have read a good deal, and am reading more, and future drafts will reflect that.

Is it morally wrong, or morally permissible, to migrate to a country illegally?

The question matters, to those who have done it, to those who feel indignation at others who have done it, to those who profit by the labor of those who have done it, to the friends and neighbors and children of those who have done it, to those who are considering doing it, and to policymakers who must decide how to deal with those who have done it or may be tempted to do it in future. But above all, it matters to those who are faced with the choice: should I migrate illegally to a foreign country or not?

To be faced with this as a live option at all, a person must be in a position such that they want to migrate illegally. That is, considering all other factors, migrating illegally must seem to them better than their other options. In particular, (a) they think either they would be better off living in another country, even illegally with all the risks and inconveniences that entails, or that they can benefit others they care about by doing so, or both; and (b) they either cannot get permission to do so from the government of that country, or can do so only excessive cost and inconvenience. Usually, though, illegal migrants seem to be people who had no realistic option of migrating legally, even at great cost and inconvenience.

The question at hand is: If a person wants to migrate illegally (in the sense specified), should they not do so for specifically moralreasons? Presumably the answer is not an unqualified yes or no, since one can invent extraordinary cases in which the act of illegal migration is clearly morally right or morally wrong.  If a migrant’s goal is to commit a terrorist attack, or steal, or abandon a wife and family, or escape justice after committing a heinous crime, or avoid paying burdensome but quite affordable debts, then he is clearly in the wrong. If a migrant is being hotly pursued by a gang of killers and crosses an international frontier in a desperate effort to save his life, or if he has secret information about an imminent terrorist attack which, if he can only arrive at the spot in time, he can prevent, saving millions of lives, there can be little doubt that the act of illegal migration is justified. The real question is how much, and what kind, of moral weight the law has in determining whether particular acts of migration are right or wrong.

There seems to be a widespread feeling that, except in strange and extreme cases, it is simply wrong to disobey the law per se, as if anything “the government” (whatever that means) forbids (requires) magically becomes morally impermissible (obligatory) for all of “its” citizens/subjects. I have this feeling myself, but as I can’t justify it directly, I take it that the generalization “it is wrong to disobey the law” holds (usually) true for a variety of often overlapping reasons that, between them, cover most of the cases. Most, but of course, not all. I don’t think anyone really holds that it is always wrong to disobey the law. As a Christian, I am not at liberty to hold that view, since the prophet Daniel and many other Biblical heroes violated human laws that were contrary to the laws of God, and many, many Christian saints were martyred for refusing to obey the law by worshipping the Roman emperors.

Recently, I was discussing the duty of obeying the law with my father, a law professor, and he seemed to recall that in the past I had expressed strong scruples about disobeying the law as such. I told him, that had never been my position, and that my most general reason for obeying the law is to avoid the temptation to lie to escape detection. But afterwards, I wondered whether I really had held the position he remembered, and if so, what arguments I had for it, that I might have forgotten. In a way, I would like to hold that position, since my complex of arguments for obeying the law seems to differ a bit from the historic position of most Christian churches, as far as I am able to discern it. I have the sense that they felt obeying the law was wrong as such, except when conscience forbade it, as in the case of the prophet Daniel or the Christian martyrs, rather than that it is usually wrong for a variety of indirect reasons. But I can’t see a way of justifying the attitude that seems most typical of Christians in the past. Not that this threatens any crisis of faith. The best arguments I can offer get me close enough for comfort to what is in any case only a rather imprecise perception of what most of my fellow Christians have thought. But if I did at some point find reasons for advocating a more robust and inherent duty to obey the law, I’d be interested in what they were. Anyway, here’s what I have to offer right now.

One reason to obey human laws is that they may coincide with natural laws. Thus, one should not murder, regardless of whether the law forbids murder or not. But as human laws do seem invariably to prohibit murder, we assimilate our condemnation of murder into a general condemnation of “breaking the law.” Likewise, one should not steal, whether the laws protect property or not, but human laws reinforce this duty. However, while killing is an objective fact quite independent of any government definitions or decisions about it, I don’t think government can be made irrelevant to the business of defining property rights. Some property rights really are simply natural rights. If a man settles on wild land to which no one had a previous claim, and cultivates it to feed his family, his property rights to that land are natural in a simple and readily perceivable sense. (This insight is associated most famously with John Locke.) But in complex commercial societies, it is not practical to establish consensus about property right by tracing all of them to such elemental origins, and courts and laws and judges are indispensable aids in defining and agreeing upon who owns what. Still, the duty not to steal is part of natural law and would apply even in the absence of government, and the reason to respect property rights remains fundamental and pre-political even when political actors have helped to adjudicate who owns what.

A second, related reason to obey the law is that it serves as evidence of what the natural law is. Suppose that action A does not seem to me to violate the natural law, but the government of the country I live in has prohibited action A. Suppose further that I view the government of my country as generally just and reasonable. I may then judge that, if judges and legislators have seen fit to make action A illegal, they probably have some good reason for thinking action A is a violation of natural law, which I happen not to have understood. I should try to understand it, but meanwhile, I should obey the law, to reduce the risk of doing something wrong. Of course, this argument only applies inasmuch as the government is generally just and reasonable. If I live under a crazy, arbitrary, absolutist king or dictator, and the laws reflect his mere random whims, the law of the land ceases to be evidence about the content of natural law, and this reason for obeying it disappears.

Modern democracy presents an interesting case here, because modern democracies typically claim to be enforcing, not the natural law, but the “will of the people,” whose “sovereignty” consists in being able to make whatever laws they like. That I have moral reasons to obey the natural law is a tautology, since by the natural law I mean the moral law. But the “will of the people,” even if the concept itself were not naïve, has no power morally to command. A man ought to do what is right, not what his fellows approve of, unless he is fortunate enough that his fellow men are wise enough to want him to do what is right. We might conclude, then, that since under modern democracy, public officials do not even claim to govern according to natural law, no one should regard their judgments as evidence about right and wrong. But I would be inclined to give democratic laws more credit than this, because I don’t think democratic publics are so corrupt as to feel they have an arbitrary, “sovereign” right to make any laws they like. I think they know there are such things as unjust laws, and that democratic majorities have a duty not to make them. I also think that democratic majorities are reasonably good judges of what laws are just, reasonable, and appropriate, when they themselves are burdened with obeying those laws. The horror stories about the political ignorance of ordinary people miss an important point, namely, that the rule of “rational ignorance” about politics ceases to apply when a person is faced with the duty of complying with the law. Then they have an incentive to understand it, and think about it, and that makes them informed voters. But that qualification shows why the “wisdom of crowds” principle has no force when it comes to immigration laws. Voters are citizens and therefore they are not prospective immigrants, so they have little incentive or opportunity to see the law from a prospective immigrant’s point of view, in order to judge its reasonableness or lack thereof. And that is why democracies’ policies on immigration, ever since they got into their heads the baneful error that restricting it is okay, have always been wildly unreasonable.

A third reason one should obey man-made laws is because the government serves as a focal point for setting expectations, and thereby solving coordination problems. Thus, natural law has nothing to say about whether societies should make people drive on the right or the left side of the road, but it does say that whatever side others are driving on, one should do the same, for one ought not to needlessly jeopardize one’s own life or those of others. Society might be able to solve this problem in a decentralized fashion if it needed to, but surely if there is a government, there should be no objection to its taking the lead here.

The argument that one ought to obey the law because the law is serving the common good by solving a coordination problem is clearly valid here, but are there a significant number of similar cases? Daylight savings might be another example, except that it seems to have hardly any moral relevance. Money, I think, is another example. I think it is wrong to counterfeit money, though of course in a Lockean state of nature there would be no objection to making pieces of paper of a certain description, because (a) it is against the law, and (b) in this case the law is solving a coordination problem for the common good. Even some quite arbitrary and micromanaging regulations could be defended as solutions to coordination problems. For example, suppose the law regulates the size of oranges that can be sold in grocery stores. Natural law has nothing against selling very small oranges per se, but if the law has created a general expectation that oranges must be a certain size, then by selling smaller ones, I might mislead customers. But, you say, customers can see the size of oranges they are buying! All right, but what if someone is selling batteries with very little power, or appliances that emit fumes harmful to health, or building houses that have an unusually high risk of fire of collapse? Granted, some people might recognize the inferiority of these products and still buy them, but should societies not be able to opt out of at least some of the inconveniences of caveat emptor? While I would hesitate to affirm that such regulations can justify the use of coercion, certainly I think one moral reason to obey the law is that government is solving coordination problems for the common good, and you should help it to do so by following the rules.

A fourth reason to obey the law would be that one has agreed to do so through a social contract. If valid, this argument has great generality, but it depends on the social contract having some kind of reality. And it takes a heroic effort to maintain that the social contract has any reality in the face of the obvious fact that we never actually sign one. Yet I do tend to make somewhat reluctant and embarrassed attempts to argue this, because I think we need at least some legitimate government (albeit we could do just find with a good deal less of it than we have), and the social contract is the governed countries, do in fact morally will for there to be a government rather like the one they have. Even if their permission is never asked, they do give their permission through their intentions and attitudes and desires and states of mind. And the manner in which they occasionally ask for its assistance carries a sense of entitlement that reflects their real sense of duty to, and their intention to, uphold their end of the bargain. I might try to argue that many gratified Constitution, but some others too, have a historic warrant from some sort of old social contract. I would then try to argue that such commitments can be presumptively passed on from generation to generation, unless explicitly and conscientiously repudiated, since we owe so much to our parents and may be regarded as having a duty, in return, to uphold the commitments that they regarded as valuable and important, inasmuch as conscience permits us to do so. Probably the sum total of these arguments would still be a bit lame, but they might have a little bit of force, and what force they have favors obeying the law.

A fifth reason to obey the law is that to break the law may involve lying, or an intention or temptation to lie under certain circumstances. The penalties governments impose on lawbreakers are usually sufficient to make lawbreaking a bad plan, except for those who expect to escape detection. Detecting lawbreakers would be easy if everyone always told the whole truth. The government would only have to ask you whether you did it. Of course, there is a difference between telling the whole truth and not lying. It is not lying to refuse to answer an unwelcome question. Often, a lawbreaker is never asked whether he broke the law or not, so he does not have to lie, or even to refuse to answer. But he certainly might be asked, and he deserves little credit for not lying if he intended to do so at need, but simply never found it necessary. There is a danger, too, that without directly lying, one might deceive by allowing falsehoods to be assumed true. Depending on the circumstances, this might be almost as culpable as a direct lie. All this lends to lawbreaking a strong aura of dishonesty, and one’s duty to the truth is a strong reason to obey the law.

Civil disobedience stands out as a case where, far from being dishonest, breaking the law is uniquely and specially truthful. The whole point of civil disobedience is that one does not try to escape detection and punishment. On the contrary, civil disobedience tends to be deliberately public, and one submits willingly to whatever punishments the oppressor chooses to perpetrate, hoping that the moral burden of administering unjust punishments will break the oppressor’s will and cause him to repent. I don’t think civil disobedience has to be deliberately public, but I do think it has to be resolutely honest. One can be civilly disobedient without actually courting arrest, or advertising one’s lawbreaking. But one has to speak about it openly, and avoid any deceit.

A sixth reason to obey the law is simply that you should presumptively comply with any request that anyone makes of you, including if that anyone is a government. Of course, this presumption isn’t a very strong reason for action. If someone asks you to, say, give them a ride to work, you probably should if it’s no great inconvenience, but it doesn’t take much to override that. It may be no great sin to refuse even if your only reason is that you’re very tired, or your favorite TV show is about to come on. Still, one reason to pay taxes (for example) is just that the government says it needs the money, and it’s usually good to be obliging when someone requests something of you.

Now, how do all these reasons for obeying the law affect the ethics of undocumented immigration?

One reason that I’m unusually lenient in my attitudes towards migrating illegally is that I put a lot of weight on the social contract as a reason for obeying the law, and this argument doesn’t apply to foreigners. If it’s difficult to defend the claim that an American should obey US laws because they’re part of a social contract, to say that a foreigner should obey US laws because of a social contract is an obvious non-starter.

To save space, I’ll dismiss the first two arguments by saying that migrating illegally is not against the natural law, and that the judgments of democratic legislators on this point are of negligible value, because they are serving voters who are not subject to the immigration laws they vote for through their representatives. Of course, there’s more to be said, and I even think some vague and highly attenuated version of the “collective property rights” might have a little force, such that migrants might act unjustly if, after migrating, they made no effort to assimilate and effectively appropriated large and important parts of a nation’s territory in such a way that natives no longer felt safe and at home there. A weak duty to assimilate might also arise out of the coordination problems that occur when, say, ignorance of English becomes widespread. All such arguments seem hardly worthy of being put in the scales against the desperate economic needs of migrants who need to feed their families or earn the money to pay for essential medical care, but they may have a (very) little force.

The sixth argument, the argument that one ought presumptively to comply with any request, is obviously weak, but if it were really the case that no one in a country wanted you there, that might be a pretty good moral reason not to go. In practice, though, the people most directly concerned with an immigrant’s decision usually want him to immigrate. Thus, Mexican migrant workers are declared illegal by the government, but welcomed by the growers, and probably by landlords, grocers, and churches as well. So I don’t think the sixth reason to obey the law has any force in most cases.

By far the strongest reason not to migrate illegally comes from the duty not to lie. To that, I’ll return. But first, let me say that there do seem to be a few weak reasons why a migrant should obey the laws of a country he wants to migrate to, and if there is not at least something to put in the moral scales against them, I would hesitate to condone an act of illegal migration. Suppose, for example, that an affluent Bostonian has a perfectly satisfactory life in the US, but has a fancy to live in Toronto. Canada won’t give him a work visa, but he still wants to go, so he moves to Toronto and works on the black market. I can’t find it in myself to judge this hypothetical person. I rather like his spirit of adventure. But I probably would advise a person against taking the moral risk of breaking the law for so casual and non-compelling reason.

In more typical cases, illegal migration is motivated by real economic desperation. No jobs at home. A family to feed. Maybe fear of religious persecution, or gang warfare. Scanty earnings are channeled into remittances. Or parents make huge sacrifices, living in the shadows for decades, so that their children may have a better life. All such morally serious reasons for illegally migrating easily override the weak arguments against it, except for the argument from truth, to which we now turn.

If we accept the absolute duty never to lie (admittedly a controversial claim), does that rule out illegal migration? Is it possible for an illegal immigrant to live in truth? Can one navigate modern life in America, or Europe, or elsewhere, without legal status, and without lying?

It seems to me that it would be almost impossible to be an illegal immigrant without using falsehoods in various formal and bureaucratic contexts. For example, one might get work, or a driver’s license, using a fake Social Security card. The question is whether there is such a thing as a morally permissible legal fictionwhich can be used without lying. I hope there is, because I often use legal fictions myself. Case in point: If one engages in online commerce, one will often have to click boxes saying “I have read the terms and conditions,” in order to complete a transaction. In these cases, I usually don’t even click the hyperlink to glance at the terms and conditions. If I do, I never read them thoroughly. I don’t think I would be capable of doing so, written as they are in mind-numbing legalese. Boredom would overwhelm my powers of attention long before I got to the end of them. So, if lying to a form counts as lying, then I tell lies all the time. Is that a sin? Should I shun online commerce, on pain of being a liar?

I don’t think so. It would probably be a better world if our understandings of consent were modified such that the types of contracts we recognize as valid were calibrated to what people could reasonably be expected to understand. But our current institutions routinely make use of “I have read the terms and agreements” as a legal fiction, and we do not really expect people to do so. By the same token, it is well-known that fake Social Security cards are widely used in the economy, and I think there are some industries in which employers routinely accept fake Social Security cards. They may prefer not to be made explicitly aware that a given employee is illegal, to avoid culpability, but they would not be surprised to discover it, or consider themselves deceived. In these contexts, to present a Social Security card is not to assert, “I am such-and-such a person,” but simply to give an employer a means to clear a bureaucratic hurdle. It therefore does not qualify as lying, and is not inconsistent with the duty of living in truth. Of course, the bureaucrats to whom the Social Security number will be reported, and the politicians and voters who stand behind them, really do want to know the truth. But they are not morally present in the situation, because they are not available to be reasoned with. To have the right to be told the truth to, one must be available to listen to the whole truth. In the same way, if I were face-to-face with a representative of the companies I engage in online commerce with, I would say, “I can’t really read this agreement, you know. It’s exorbitantly long and I’m not a lawyer.” But a form is not a human being and doesn’t have the same right to be told the truth. The people behind the forms forfeit the right to be told the truth if they demand information in unreasonable ways, and are not available in person to be held accountable for their unreasonableness.

Even if it is sometimes morally permissible to use fake Social Security cards, the duty of telling the truth will doubtless involve extra risk and sacrifice for those who migrate illegally, over and above what they would face by being here without any scruples about lying. There may be jobs a person cannot conscientiously take, because conventions have not given the presentation of a Social Security card the nature of a legal fiction. One might have to tell such employers the card was fake, to avoid really deceiving the employer. Social relations might also involve special dangers. You never know who might be a tattle tale, but again, you can’t lie.

So, to someone who was considering migrating illegally, but was not sure whether this was a morally acceptable thing to do, I would advise them to examine themselves and make sure that they were really determined not to tell any lies in the process, with the tricky but important exception of legal fictions. I would advise them to think of themselves as engaged in conscientious civil disobedience, and to err on the side of telling more of the truth than honesty demands. I would ask them if they had the courage to tell the truth at great personal risk, and the magnanimity to face the injustices of the system, should they be arrested and deported, without rancor or bitterness, and in a spirit of love and forgiveness. If not, I would advise them not to migrate illegally.

The claim that open borders would “double world GDP” is one of our side’s better talking points. Of course, it’s just a guess, based on theoretical models calibrated to the data, which amounts to a sophisticated, but still very fallible, form of extrapolation. These models are easy to mock if you understand them well enough to see their weak points. Yet, what alternative is there? The question of what the global economic impact of open borders would be is interesting enough to be worth answering tentatively. I’ve been working on my own, which has evolved somewhat since I wrote about it a few months ago. Meanwhile, I came across a new one, “The Global Welfare and Poverty Effects of Rich Nation Immigration Barriers,” by Scott Bradford (2012).

First, Bradford’s conclusions. Under open borders (with an exponential distribution of skills, more realistic than the uniform distribution that Bradford also considers), total world output would rise from $74 trillion to $130 trillion. Not quite “double world GDP,” but a more than 75% increase. Wages in rich countries would fall by 7.5%. Since Bradford, like John Kennan, does not model human capital as an independent factor of production, but simply interprets “skill” as multiplying a person’s labor power, this 7.5% wage drop would equally affect workers at all skill levels. There would be a 46% increase in wages for those who stayed in poor countries, and migrants to rich countries would see their wages rise by 157%.

Bradford chooses to focus on the poverty impact of open borders, but this turns out to be sensitive to an assumption about the inherent fixed cost of migration. If this cost is $10,000, the fraction in poverty would fall by 66%. Raise it to $20,000, and poverty is reduced by only 42%.

Now for the model’s Achilles heel:

[The model] implies that 94-97% of the poor region workforce, or about 2 billion workers plus their depends, would move to [the rich countries] if they could. That is unrealistic. As long as total factor productivity is higher in the rich region, and capital can move along with labor, our analysis implies that the great majority of poor region workers would be economically better off, and would increase world output, if they could move freely to the North. Even if the results in this paper are off by an order of magnitude due to elements not captured by our simple model, opening up migration has great potential to boost incomes around the world.

Where does this concession leave the model? If the author’s verdict on his own projections of migrant numbers is “That is unrealistic,” then what exactly is he claiming? He can’t be claiming that the prediction of 94-97% migrating won’t come to pass, but the prediction of raising world GDP by 75% will, since the latter depend logically on the former. What does the “even if the results in this paper are off by an order of magnitude…” sentence mean? It could be read as, “For some reason that I don’t really know, let’s assume ten times fewer people would migrate. If the effects are proportional, you’d still see a big increase in global incomes and a lot of poverty reduction.” But to conclude with such vague hand-waving as that seems to render pointless the paper’s effort to give a logically precise description of the world and assign precise, empirically-grounded values to certain parameters and variables. If the predicted migration flows are unrealistic, then the model is leaving out something important– or many things. If those things were understood and incorporated, we have little reason to think the model’s other results would be preserved, or scaled down in any predictable way.

Actually, given his other assumptions, Bradford’s estimates of the number of migrants are, if anything, indefensibly low. You might ask how 90%+ of the population could afford to migrate at all if migration costs are assumed to be $10,000 or $20,000. But Bradford’s migrants optimize an intertemporal utility function, and migration is a long-term investment in living in a better place. But it’s hardly plausible that the cost of migration would be $10,000, let alone $20,000. Bradford cites empirical evidence for this, but here, extrapolation is illegitimate. If only a skilled elite is migrating, they’ll do it in a relatively comfortable and expensive way. Under open borders, there’d be economies of scale in the migration process itself, and mass migration would find the cheapest ways to move. You would expect, for example, to see a revival of people traveling by ship. There’s no point in that now, because anyone who can hope to travel internationally values their time enough to prefer a plane ticket and a few hours’ journey to spending weeks on a boat. The market for international passenger travel by sea would be tiny. Under open borders, with billions of poor people on the move, ocean-going ships would offer international travel for a fraction of the cost of a plane ticket. So even the fig leaf of respectability that Bradford’s model derives from the 3% of people in poor countries that are predicted to stay put, we must take away. (I think a tiny number of poor people would still stay home without that, merely for the sake of the cheap land left behind by the mass exodus.)

I don’t want to come across as too negative, though, because I know by experience how difficult it is to do what he is attempting. You can’t project what the global distribution of income would be like under open borders without first having a fairly thorough explanation of what it is like now. You really need a theory of the wealth and poverty of nations even to get a model of the global economic impact of open borders off the ground. And economists haven’t exactly covered themselves in glory by their successes in explaining the wealth and poverty of nations.

Bradford (2012) could have followed Kennan (2012) by simply assuming that “strong attachment to home locations” will prevent everyone from wanting to move, and then adopting an arbitrary assumption, or an assumption with very weak empirical motivations, about what share of people would. I respect Bradford’s frankness about his model’s failure to predict realistic numbers of migrants as much as (not necessarily more than) I respect Kennan’s ad hoc measures to reduce the number of migrants his model predicts. The question which brings both of them to grief, in different ways, is: Given the opportunity to migrate to countries that are much more productive and have higher standards of living, why would anyone stay home? It’s not that answers to this question are difficult to propose. The trouble is that it’s very hard to quantify them, even in the loosest and most arbitrary way.

So, can I do better? I think so. My model will include human capital as an explicit factor of production; economies of scale at the city level; and differences in the cost of capital across countries due to country risk premiums. But what it will predict, I won’t know until I’m done calibrating it. Stay tuned!