Diminishing Marginal Utility and the Redistributive Urge

It is a staple of economic thought that the additions to utility (enjoyment, satisfaction, happiness, pleasure) gained from additional income or wealth diminish as income or wealth increases. From this assumption flows a theoretical justification for the redistribution of income or wealth from persons of high income or wealth to persons of lower income or wealth.*

It follows — if you accept the assumption of diminishing marginal utility and ignore the negative effect of redistribution on economic growth — that overall utility (a.k.a. the social welfare function) will be raised if income is redistributed from high-earners to low-earners, and if wealth is redistributed from the wealthier to the less wealthy. But in order to know when to stop redistributing income or wealth, you must be able to measure the utility of individuals with some precision, and you must be able to sum those individual views of utility across the entire nation. Nay, across the entire world, if you truly want to maximize social welfare.

Most leftists (and not a few economists) don’t rely on the assumption of diminishing marginal utility as a basis for redistributing income and wealth. To them, it’s just a matter of “fairness” or “social justice.” After all, “you didn’t build that,” according to America’s Glorious Leader. It’s odd, though, that affluent leftists seem unable to support redistributive schemes that would reduce their income and wealth to, say, the global median for each measure. “Fairness” and “social justice” are all right in their place — in lecture halls and op-ed columns — but keep them at a comfortable distance from an affluent leftist’s comfortable abode.

In any event, those leftists who deign to offer an economic justification for redistribution usually fall back on the assumption of the diminishing marginal utility (DMU) of income and wealth. In doing so, they commit (at least) four errors.

The first error is the fallacy of misplaced concreteness which is found in the notion of utility. Have you ever been able to measure your own state of happiness? I mean measure it, not just say that you’re feeling happier today than you were when your pet dog died. It’s an impossible task, isn’t it? If you can’t measure your own happiness, how can you (or anyone) presume to measure and aggregate the happiness of millions or billions of individual human beings? It can’t be done.

Which brings me to the second error, which is an error of arrogance. Given the impossibility of measuring one person’s happiness, and the consequent impossibility of measuring and comparing the happiness of many persons, it is pure arrogance to insist that “society” would be better off if X amount of income or wealth were transferred from Group A to Group B.

Think of it this way: A tax levied on Group A for the benefit of Group B doesn’t make Group A better off. It may make some smug members of Group A feel superior to other members of Group A, but it doesn’t make all members of Group A better off. In fact, most members of Group A are likely to feel worse off. It takes an arrogant so-and-so to insist that “society” is somehow better off even though a lot of persons (i.e., members of “society”) have been made worse off.

Would the arrogant so-and-so agree that “society” had been made better off if I were to gain a great deal of satisfaction by punching him in the nose? I don’t think so, but that’s the import of his redistributive arrogance. He could claim that my increase in happiness doesn’t cancel his decrease in happiness, and he would be right. But that’s as far as he could go; he couldn’t claim to measure and compare my gain and his loss.

The third error lies in the implicit assumption embedded in the idea of DMU. The assumption is that as one’s income or wealth rises one continues to consume the same goods and services, but more of them. Thus the example of chocolate cake: The first slice is enjoyed heartily, the second slice is enjoyed but less heartily, the third slice is consumed reluctantly, and the fourth  slice is rejected.

But that’s a bad example. The fact is that having more income or wealth enables a person to consume goods and services of greater variety and higher quality. Given that, it is possible to increase one’s utility by shifting from a “third helping” of a cheap product to a “first helping” of an expensive one, and to keep on doing so as one’s income rises. Perhaps without limit, given the profusion of goods and services available to consumers.

And if should you run out of new and different things to buy (an unlikely event), you can make yourself happier by acquiring more income to amass more wealth, and (if it makes you happy) by giving away some of your wealth. How much happier? Well, if you’re a “scorekeeper” (as very wealthy persons seem to be), your happiness rises immeasurably when your wealth rises from, say, $10 million to $100 million to $1 billion — and if your wealth-based income rises proportionally. How much happier is “immeasurably happier”? Who knows? That’s why I say “immeasurably” — there’s no way of telling. Which is why it’s arrogant to say that a wealthy person doesn’t “need” his next $1 million or $10 million, or that they don’t give him as much happiness as the preceding $1 million or $10 million.

All of that notwithstanding, the committed believer in DMU will shrug and say that at some point DMU must set in. Which leads me to the fourth error, which is an error of introspection. If you’re like most mere mortals (as I am), your income during your early working years barely covered your bills. If you’re more than a few years into your working career, subsequent pay raises probably made you feel better about your financial state — not just a bit better but a whole lot better. Those raises enabled you to enjoy newer, better things (as discussed above). And if your real income has risen by a factor of two or three or more — and if you haven’t messed up your personal life (which is another matter) — you’re probably incalculably happier than when you were just able to pay your bills. And you’re especially happy if you put aside a good chunk of money for your retirement, the anticipation and enjoyment of which adds a degree of utility (such a prosaic word) that was probably beyond imagining when you were in your twenties, thirties, and forties.

In sum, the idea that one’s marginal utility (an unmeasurable abstraction) diminishes with one’s income or wealth is nothing more than an assumption that simply doesn’t square with my experience. And I’m sure that my experience is far from unique, though I’m not arrogant enough to believe that it’s universal.

Thus endeth today’s lesson in economics and humility.

* It is a misconception that demand curves slope downward and to the right because of DMU. They do not, as explained by Bruce R. Beattie and Jeffrey T. LaFrance in “The Law of Demand versus Diminishing Marginal Utility,” which is available here as a PowerPoint presentation.

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Related posts:
The Social Welfare Function
Inventing “Liberalism”
Accountants of the Soul
Enough of “Social Welfare”