The burden of a tax falls on whoever cannot get away from it. This is the whole secret of incidence, and once it is grasped the rest is detail. A tax drives a wedge between what the buyer pays and what the seller keeps; the wedge opens toward whichever party is less able to escape — to substitute, to abstain, to take its money or its labor or its custom elsewhere. The side with alternatives shifts the burden; the side without them bears it. Economists call the capacity to flee elasticity and dress the matter in curves, but beneath the curves lies something plainer and harder: that to be unable to escape a tax is to be, in the relevant sense, without power — and that the question of who pays is, in the end, a question of who is free to walk away.
The companion plate established the wedge and the negative truth that the law does not fix how it divides; this plate supplies the positive one. What the law leaves open, elasticity settles, by a rule both simple and exact: the burden divides between the two sides in inverse proportion to their elasticities, the less elastic a party, the larger its share. The reasoning is plain once the wedge is seen as a contest of withdrawal. When the tax raises the buyer's price and lowers the seller's, each would retreat from the worse terms — but the one who can retreat easily, cutting his quantity sharply at a touch, will not sit still for a bad price, and so it is forced upon the one who cannot, who goes on much as before. At the limits the rule is starkest. A party perfectly inelastic — who trades the same quantity whatever the price — bears the entire tax, absorbing any terms without flinching; a perfectly elastic one — who vanishes at the smallest move against him — bears none, the slightest attempt to shift it driving him off. Between these poles every real division falls, and where it falls is fixed by how readily each side can flee.
But to say that the inelastic bear the tax is only to restate the puzzle in technical dress, for it invites the further question: what makes a party inelastic? The answer is that elasticity is not a primitive trait but a measure of alternatives. A buyer is elastic when he has substitutes — other goods that serve, other sellers, the option of going without; inelastic when he has none, the good a necessity with no replacement and no tolerable absence. A seller is elastic when he can take his capital, labor, or land to some other use that pays as well; inelastic when this is the best he has and the alternatives poor. Elasticity, in short, is the range of one's options reduced to a number — and the range of one's options is a fair definition of one's freedom, and not a bad one of one's power. Albert Hirschman gave the faculty its name when he called it exit: the ability to leave a relationship that has turned against you, which both spares you its costs and disciplines the party who would impose them. The elastic can exit; the inelastic are held in place; and a tax, like every other burden, comes to rest on those who cannot leave.
The most consequential instance of the rule is the oldest quarrel in the theory of taxation: the incidence of a tax on capital. Capital is, of all the factors of production, the most elastic in the relevant sense — the most able to flee. It moves from one industry, country, or form to another with a speed that has only increased as the world's markets have knit together; Adam Smith saw the principle two centuries before the electronic transfer, observing that the owner of capital is properly a citizen of the world, attached to no country, who will remove his stock from any land that exposes it to a vexatious tax and carry it where it is used more gently. Labor, by contrast, is the least elastic of the factors — the most bound. The worker has one country, usually one city, a family and a language and a life rooted in a place; he cannot, as capital can, dissolve and reconstitute abroad at the close of business. From this asymmetry follows a conclusion that surprises every student who meets it: a tax laid upon capital need not be borne by capital at all. If capital flees until its after-tax return is restored to what the world offers, then something else must give — and what gives is the wage of the labor that cannot flee, so that a tax on the mobile factor settles, in some measure, on the immobile one.
What holds for capital and labor holds wherever a tax is laid, for the same asymmetry of escape recurs in market after market. A tax on a necessity — bread, fuel, the medicine a sick man must have — falls almost wholly on the buyer, who has no substitute and cannot abstain, while a tax on a luxury easily forgone is absorbed in good part by the seller, who would sooner give up his margin than watch his customers leave. A tax on the only employer in a company town is borne by workers who cannot leave it; a tax that a footloose enterprise can escape by relocating is borne by whatever is rooted to the spot. In every case the burden performs the same migration, away from whoever can flee and toward whoever is held fast. And the migration has a troubling tendency, for the things that cannot be escaped are very often the things the poor depend upon — the necessities they cannot substitute, the labor they cannot move, the place they cannot leave. The burden of taxation, left to the market, drifts toward the bottom not by malice but by mechanism: it seeks the inelastic, and the inelastic are disproportionately those with the fewest alternatives, which is to say the least.
And so the incidence of a tax, which wears the look of a technical fact — a matter of elasticities and curves, to be computed and not contested — is a fact of a very different kind. A price is a verdict on a hidden contest, mistaken for a fact of nature; and the after-tax price, which carries the burden of a tax to its resting place, is a verdict of exactly that sort. It distributes the burden according to who can walk away and who must stay — and that distribution, which the economist records as a ratio of elasticities, is in truth the outcome of a contest over escape that the curves measure without naming. The elasticity that appears in the formula as a neutral parameter is, at the level that decides who suffers a tax, the encoded measure of each party's power to flee — how many alternatives he commands, how mobile he is, how far he can do without the exchange. To read the incidence of a tax off the elasticities is therefore not to escape the question of power but to answer it in cipher: the verdict on who pays is a verdict on who is free, transcribed into the language of curves and mistaken, by those who read only the curves, for a fact about goods.
It will be objected that this dresses a neutral mechanism in the borrowed clothes of politics. Elasticity, the objection runs, is a technical property of preferences and technologies, not a measure of power: the demand for insulin is inelastic because of what insulin is, not any powerlessness in the patient; the supply of capital elastic because of the nature of capital, not any privilege in its owners. To call inelasticity powerlessness is to smuggle a moral charge into a morally neutral fact. And there is a second objection, sharper still: it may be positively good that the inelastic bear the tax. The plate that follows, on the excess burden, will show that the deadweight loss of a tax is smallest when it falls on what cannot flee, since a tax that changes no behavior wastes nothing — from which the rule of optimal taxation, due to Frank Ramsey, counsels raising revenue by taxing the inelastic most heavily of all. If efficiency itself directs the burden toward the captive, then the captive's bearing it is no scandal but a sound design, and the language of a contest over power merely sentimentalizes a question of arithmetic.
The objection is right about a single market and wrong about the whole. Grant that the inelasticity of insulin is a fact about insulin: it remains true that whether one's wants run to inelastic necessities or elastic luxuries, whether one's livelihood is mobile or rooted, whether one can relocate or must stay, are not facts about goods but about persons — and they track, with grim reliability, the resources those persons command. The rich are elastic across the board — they can substitute, defer, relocate, and wait, for wealth is precisely the possession of alternatives; the poor are inelastic across the board, bound to the necessity, the job, the place, for poverty is their absence. The distribution of elasticities over a population is thus no neutral fact but a map of the distribution of options, which is to say of power; and the insulin case displays it, for the patient's inelastic need is exactly his powerlessness in that exchange. As for the efficiency argument, it does not soften the conclusion but sharpens it to a point: the Ramsey rule counsels taxing the captive precisely because he cannot flee, so that the most efficient tax is, by construction, the one that falls on the powerless. Whether that is good design or a quiet injustice is the question the volume must hold open — but it is not a question elasticity has answered; it is one elasticity has disguised.
This is why the escape is the volume's deepest lesson: it shows that the resting place of every tax is fixed by flight, and flight by power. A price is a verdict on a hidden contest, mistaken for a fact of nature; and the after-tax price is such a verdict, settling the burden upon whoever cannot get away and reporting the settlement as a ratio of elasticities, a fact about goods, a piece of arithmetic. To learn who truly pays a tax is to learn who is free to leave — and that knowledge, once the curves are read for what they encode, is a map of mobility and its absence: of who commands alternatives and who has none, who can flee the burden and who must shoulder it for want of anywhere to go. The statutory question — who is charged? — the last plate dissolved. The deeper question — who bears? — this one answers, and the answer is always the same in form: whoever cannot escape. Beneath every schedule of rates and every diagram of curves, the question of who pays a tax is the question of who is free; and a society that wishes to know what its taxes really do must learn to read the one as the other.
A tax settles on whoever cannot walk away from it. To know who really pays it, do not read the statute — ask who is free to leave.
The wedge is driven, and it opens, we now see, toward the one who cannot flee. What remains of the volume is the working out of this single fact through the instruments by which societies tax. The next plate measures the cost of the flight itself — the trades that never happen because the elastic withdraw, the value a tax destroys over and above the revenue it raises. After it come the rules that would aim the burden deliberately: the inverse rule by which efficiency would direct it at the captive, the ladder by which fairness would lift it from them; the toil of labor and the ground of land, the most bound of factors and the one that cannot move at all; and, at the last, the question of what the whole apparatus is for. Through all of them the escape remains the master key — for to tax is to lay a burden, and a burden always rolls downhill, toward whoever is rooted to the spot. The argument remains open.