Fiscal Fictions #5: Taxes Discourage Investment
A Dialogue on Taxation, Full Expensing, and the Neutrality of Capital Investment
Does taxing the returns to capital investment necessarily discourage investment? The question is confidently answered in almost every Econ 101 classroom: of course it does. If the state takes a portion of what an investment earns, the investor keeps less, and some investments no longer justify their risk. This teaching shapes practical tax policy across the modern world. What follows is a dialogue that examines whether that answer is actually correct — and discovers that the conclusion confidently taught in introductory economics, while not wrong in all circumstances, depends entirely on a question almost never asked: how does the treasury measure the income it proposes to tax?
What follows takes the form of a Socratic dialogue rather than a conventional essay. I have found that some arguments are better shown than stated, and this is one of them — the logic emerges more naturally through question and answer than through assertion. Whether that holds for you as a reader is something I am genuinely curious about, and I would welcome your thoughts in the comments.
Part One: The Wound
Socrates: Tell me, Thrasymachus, do you believe, as many do, that when the state levies an income tax on a business, it discourages the owners from investing in new machinery?
Thrasymachus: Of course it does, Socrates! Every merchant in the republic knows that investors demand a certain yield — let us say ten percent per annum after any taxes — to justify the risk of parting with their gold. They demand this because they believe they can earn that much from other, comparable investments elsewhere in the republic; if a merchant cannot match that return, investors’ gold will go where it is better rewarded. Taxation adds a financial burden that the investment must somehow bear: the merchant must now earn enough not only to satisfy his investors but also to pay the tax. Unless the machine can clear that higher bar, the investment will not proceed. Capital flies from our markets to places where the treasury is less greedy.
Socrates: Let us test your claim with arithmetic before accepting it as settled. Suppose a merchant wishes to purchase a new machine for one hundred gold pieces. His investors demand a ten percent after-tax return — meaning, on one hundred pieces committed, they must receive ten gold pieces of profit each year to justify the venture. The treasury’s system of taxation levies a tax of twenty percent on the machine’s annual earnings. How many gold pieces must be earned each year through use of the machine, after all labor and operating costs are paid, to leave the investors their required ten?
Thrasymachus: Why, twelve gold pieces, surely — ten for the investors and two for the tax.
Socrates: Let us check that figure. If using the machine earns twelve gold pieces, the treasury takes twenty percent of twelve — that is two and two-fifths pieces, not two. The investors are left with nine and three-fifths pieces, which falls short of their required ten.
Thrasymachus: Then we need a little more — ten for the investors plus two and two-fifths for the tax — call it twelve and two-fifths pieces?
Socrates: And if the machine’s use earns twelve and two-fifths pieces, the treasury takes twenty percent of that — two and nearly one-half pieces — and your investors receive just under ten. You are chasing a moving target, Thrasymachus. The tax applies to the full earnings from using the machine, including whatever portion was meant to cover the tax itself. The correct figure is twelve and one-half gold pieces. At that level, the treasury takes exactly two and one-half pieces, and the investors receive precisely ten.
Thrasymachus: I see — the calculation is self-referential. If the tax is twenty percent, the investors will keep eighty percent of the total earnings. If the investors’ share must be at least ten gold pieces, we can divide ten by eighty percent to find that the minimum required earnings is twelve and one-half pieces.
Socrates: Just so. The twenty percent tax has raised the investment hurdle from ten percent to twelve and one-half percent of the capital committed. Now consider our merchant. The best available machine of this type, when put to use, earns ten gold pieces on one hundred invested — a perfectly respectable ten percent return in a world without tax. Under the treasury’s twenty percent levy, that machine now falls two and one-half pieces short of what the investors require. The investment does not get made.
Thrasymachus: And surely the damage falls on the merchant, his investors, and his customers — the merchant forgoes the profit he might have earned, the investors forgo the return they sought, and the customers will find fewer or worse products on offer. It is a loss, certainly, but a contained one.
Socrates: The damage reaches further still. Consider the blacksmith who would have built and sold the machine — he now has no buyer. He earns nothing on this transaction and pays no tax on that nothing. The workers the merchant would have employed to operate the machine remain idle. And the treasury, which sought revenue by taxing the merchant’s profits, finds it has instead destroyed the very transaction it hoped to tax — collecting nothing from the merchant, nothing from the blacksmith, nothing from any of the chain of transactions that would have followed. In reaching for more, it has collected less.
Thrasymachus: The treasury has not merely failed to collect its share — it has destroyed the wealth from which that share could have been drawn. Everyone is poorer: merchant, investors, blacksmith, worker, customer, and treasury alike.
Socrates: Economists call this a deadweight loss. It is not a transfer of wealth; it is a loss of the opportunity to create wealth. The state did not take the two and one-half pieces it sought — it destroyed the twelve and one-half pieces the investment would have generated, and collected nothing.
Thrasymachus: Then perhaps the remedy is what the treasury’s own learned advisors would counsel — and what the merchants’ guilds and the senate’s finance committee have long agreed upon: do not abandon the tax, but calibrate it carefully. Set it at a rate moderate enough that most investments still proceed and the republic collects a meaningful revenue. Surely between confiscation and nothing lies a wise and practical middle ground, endorsed by the best financial minds of the age.
Socrates: Let us ask what that means precisely. Start from zero — no tax at all. The machine that, when put to use, earns ten pieces on one hundred invested clears its hurdle exactly, and no investment is killed. Now introduce any tax at all: the hurdle immediately rises above ten pieces, and some marginal investments — the ones that just barely cleared the hurdle before — begin to fail. At twenty percent, we have already established that the machine must earn twelve and one-half pieces. As the rate climbs further, so does the hurdle — sixteen and two-thirds pieces at forty percent, twenty-five pieces at sixty percent, fifty pieces at eighty percent, one hundred pieces at ninety percent. There are only rates that make it more or less severe. There is no moderate rate that eliminates the wound.
Thrasymachus: Then under this accounting, the only non-distorting tax rate is zero. My original claim is vindicated: any tax, at any positive rate, under this system kills some investments that would otherwise have been made.
Socrates: You are vindicated — under this system. And under this system, the damage is worse still than we have yet shown. I ask you to hold that phrase in mind: under this system. For the system itself is what we shall soon have reason to question. The harm is not merely that fewer investments proceed. As the rate climbs, the character of investment changes as well. The steady, reliable machines — those promising modest but certain returns — are killed first, since they cannot clear the rising bar. What kinds of ventures remain standing as the rate climbs?
Thrasymachus: Only those promising extraordinary returns — sixteen pieces on one hundred invested, then twenty-five, then fifty. But Socrates, I know the merchants of this republic. Machines promising such returns are either genuine marvels or outright frauds. The cautious merchant who would have bought a reliable workhorse now faces a stark choice: do not invest at all, or stake his fortune on a device whose maker promises the stars.
Socrates: The treasury’s rules have, without intending this consequence, created an investment selection effect: low-return, reliable investments are progressively eliminated, leaving only those requiring increasingly extraordinary pre-tax returns — and in commerce, extraordinary promised returns and elevated risk often travel together. And when those speculative ventures fail — as they frequently must — the treasury collects nothing from them either. The attempt to claim more has produced not revenue, but ruin.
Thrasymachus: It is a deeply perverse result. A tax intended to fund the republic has instead corrupted its commerce — degrading not merely the quantity of investment but often even the quality of what investments remain. The republic is left with fewer machines, less prosperous merchants, and a treasury that faces an impossible choice: collect nothing and leave the republic unfunded, or collect something and distort everything.
Socrates: And all of it flows from a single error in how the treasury measures what it taxes. Let me ask you a question about that error. When use of the machine earns twelve and one-half gold pieces and the treasury taxes that sum, has the treasury correctly measured the merchant’s profit from the machine’s use?
Thrasymachus: I am not sure I follow you, Socrates.
Socrates: The merchant spent one hundred pieces to acquire the machine. Eventually, as it wears out and must be replaced, he will need to recover those one hundred pieces merely to remain whole — to return to his investors the capital they committed. He has not truly profited until his cost is recovered. Yet the treasury taxed his full earnings as though the cost of the machine had already been recovered — as though it had cost him nothing at all. Was that measurement of his profit correct?
Thrasymachus: No — it taxed gross earnings rather than net earnings. It called something profit that was, in part, merely the recovery of the merchant’s own capital — the return of capital, not a profitable return on investment.
Socrates: And that error in measurement produced this deadweight loss, corrupted the composition of investment, and drove merchants toward speculation. Now — how quickly should the treasury permit the merchant to recover his cost?
Part Two: Allowance for Cost Recovery and Depreciation
Thrasymachus: Over the life of the machine, I would think. As it gradually wears out, he recovers a portion of the hundred pieces each year, and the treasury would modify its system to tax only what remains above that recovery.
Socrates: That is the natural answer, and it is an improvement. The scribes call this depreciation — the gradual allowance of cost recovery as the asset wears out over time. But consider what gradual recovery means in practice. Suppose the machine is expected to last ten years and so the treasury allows ten pieces of cost recovery each year. The merchant recovers his first ten pieces promptly — but his last ten pieces are promised a decade hence. Ten pieces of gold in hand today can be put to work immediately: the merchant can invest them, buy materials, hire craftsmen, and earn further returns. Ten pieces promised ten years from now cannot do any of that work in the interim. The promise is worth less than the coin. So even under depreciation, the treasury is still taxing a portion of the merchant’s own capital — not as brazenly as when it allowed no recovery at all, but taxing it nonetheless. The wound is smaller; it has not closed.
Thrasymachus: So depreciation reduces the wound, but does not close it. What if the treasury allowed the merchant to recover his full cost at the very moment of investment — to deduct the entire one hundred gold pieces in the year he buys the machine, in other words treating the investment as if it were just another business expense?
Socrates: That would be immediate and total cost recovery — full expensing, as some call it. But I suspect you have an objection before we proceed.
Thrasymachus: I do, and it is a serious one. If the merchant reduces his current tax bill by twenty pieces today, the treasury is left with twenty fewer pieces in its coffers to fund the republic’s current needs. The state has surrendered a sure claim on existing revenue at the very moment the merchant acts, staking those coins on a future yield that may never materialize. Surely this simply starves the public treasury today to subsidize a private gamble, with no guarantee the machine will ever yield enough to make the state whole.
Socrates: That is precisely the objection we must test. Return, then, to our same merchant, and watch where the gold actually goes.
Part Three: The Full-Expensing Remedy
Socrates: Our merchant wishes to buy the same machine — the one whose use earned ten gold pieces on one hundred invested and was killed by the treasury’s failure either to allow cost recovery or to allow it fast enough. Suppose that alongside this investment the merchant operates other profitable ventures throughout the year, from which he routinely sets aside gold to pay his expected tax bill.
Thrasymachus: A prudent merchant must always hold back gold for the tax collector, Socrates. Those twenty pieces sitting in reserve could be buying better tools or expanding the shop — if it were not for the need to save against the coming tax bill!
Socrates: Indeed. But now the treasury’s system permits full expensing. When this merchant decides to buy the machine, he realizes something about his ledger. Because the machine is fully expensable, he knows his tax liability for the year will be reduced by exactly twenty gold pieces — the twenty percent tax on the hundred piece cost he is now permitted to deduct immediately. Since he no longer needs to hand those twenty pieces to the state at year’s end, what can he do with the cash he has been accumulating in his tax reserve?
Thrasymachus: Why, he can pull those twenty pieces out of his tax reserve and use them to help pay the blacksmith for the machine today.
Socrates: Exactly. To pay the blacksmith one hundred gold pieces, he combines eighty pieces — drawn from his business savings or from his investors — with the twenty pieces he can now withdraw from his tax reserve. But tell me, Thrasymachus: if the merchant had kept those twenty pieces sealed away in his tax reserve, and a wealthy neighbor had instead walked in and placed twenty fresh pieces on the table to complete the purchase fund, what would we call that neighbor’s action?
Thrasymachus: We would say the neighbor made a new investment of twenty pieces into the firm’s capital.
Socrates: And does the blacksmith care whether the twenty pieces came from the neighbor’s purse, or from the tax reserve the state permitted the merchant to empty?
Thrasymachus: The blacksmith cares nothing for the source of the gold; he only requires the payment. The effect on the purchase fund is identical.
Socrates: Then we must agree that the state’s permission to move those twenty pieces from the tax reserve to the blacksmith has the same economic effect as if the state had invested twenty pieces of capital directly.
Thrasymachus: I cannot deny it. Mechanically, the state has placed twenty pieces into the hands of the blacksmith just as surely as if it had delivered them in a purse.
Socrates: Now the year ends. Using the machine earns ten gold pieces — the same ten that proved insufficient under the old accounting. The state takes its twenty percent tax on those ten pieces — two gold pieces — leaving eight for the investors. But here is the critical question: against how many pieces of committed capital must we measure that eight-piece return?
Thrasymachus: Against eighty pieces — the investors’ own capital. The state supplied the equivalent of the remaining twenty through the expensing mechanism.
Socrates: Eight pieces of return on eighty pieces of committed capital. What rate is that?
Thrasymachus: [Calculating] Eight divided by eighty — it is exactly ten percent.
Socrates: And what did the investors require?
Thrasymachus: Ten percent.
Socrates: By the gods! This is the same machine, the same investors, the same ten gold pieces of earnings, the same twenty percent tax rate that killed the investment when the treasury denied cost recovery — and now the blacksmith has a buyer, the merchant has a machine, the treasury collects its share, and the investors have received exactly what they required. One change — the accounting rule for cost recovery — and the wound has closed completely.
Thrasymachus: The wound was not in the tax. It was in the measurement of taxable profit.
Socrates: You have stated it perfectly. Now let us ask whether this remedy is complete — whether it holds at higher tax rates and for riskier ventures — or whether it is merely a fortunate property of these particular numbers. Recall that without full expensing, a higher rate did not merely produce more deadweight loss; it systematically drove merchants toward ventures requiring increasingly extraordinary returns. Does full expensing break that connection as well?
Thrasymachus: I suspect it cannot. If the treasury became truly greedy and raised the tax to forty percent, or if investors in a riskier venture demanded fifteen percent, surely the distortion would return.
Socrates: Let us test both objections at once. Suppose the tax rate is raised to forty percent, and we examine a riskier venture where investors demand a fifteen percent after-tax return. The machine, when put to use, earns fifteen gold pieces per year after all operating costs. When the merchant pays the one hundred gold piece cost of this new machine, how many pieces can he withdraw from his tax reserve?
Thrasymachus: The tax rate is forty percent, so he takes forty pieces from his tax reserve. He only needs to supply sixty pieces of his own capital.
Socrates: His own permanent capital at risk is sixty pieces. At year’s end, the risky machine yields fifteen gold pieces. The state collects its forty percent. How many pieces does the state take?
Thrasymachus: Forty percent of fifteen — that is six gold pieces. Leaving nine for the investors. And nine pieces on sixty committed is exactly fifteen percent return on investment.
Socrates: Just so. Now, without full expensing, how much would the machine have had to earn before tax to deliver fifteen pieces after a forty percent levy?
Thrasymachus: Fifteen divided by sixty percent — that is twenty-five gold pieces. A machine whose use earns only fifteen pieces would have been a terrible loser! Without full expensing, the forty percent rate has driven the required pre-tax return from fifteen percent to twenty-five percent — precisely the kind of extraordinary return that, as we saw, only speculative ventures dare promise.
Socrates: And yet under full expensing, that same machine clears its hurdle exactly, because the state has co-invested its forty-percent share and asks only its proportional return. The higher tax rate has not forced the merchant toward speculation — it has simply made the state a larger partner in the same reliable venture. Consider how remarkable this is, Thrasymachus. The state does not know the mind of the merchant, nor can it calculate the specific, risk-adjusted hazards of every unique shop in the republic. It need not know the cost of capital, the degree of risk, or the conditions of any particular industry. Yet blindly, simply by allowing full expensing, the state automatically co-invests at each firm’s specific cost of capital — whether it is ten percent, fifteen percent, or fifty percent. The actual tax rate completely disappears from the investment decision, and the mechanism adapts to each firm’s unique circumstances without the treasury understanding any of them.
Thrasymachus: This is a truly astonishing property of numbers. The tax system adapts itself perfectly to risk without the treasury needing to understand it. But tell me, Socrates, if a private investor advanced forty percent of the cash for a venture, and stood to lose forty percent of his funds if the project failed, would we not say he has established a participation right in that business?
Socrates: We would call him a partner — a silent partner, perhaps, since he takes no hand in managing the venture.
Thrasymachus: And would it be reasonable for that partner to expect to receive forty percent of the normal returns generated by that shared capital?
Socrates: It would be the very definition of a fair contract.
Thrasymachus: Then I must concede that because the state’s position under full expensing is functionally equivalent to such an investor’s, its claim to participate in the normal return is established. It is not acting as a thief, but as a risk-sharing participant. But what if the machine is an extraordinary success? What if, instead of the expected fifteen gold pieces, it yields super-normal returns — say, fifty gold pieces?
Socrates: Then the state takes its forty percent tax on those fifty gold pieces, which amounts to twenty gold pieces total. Six of those pieces are its share of the normal return we just justified. But it also takes fourteen pieces from the surplus. Tell me, does taking those fourteen pieces alter the minimum return required to justify undertaking the investment?
Thrasymachus: How could it? Only fifteen gold pieces of total earnings were required to justify the investment in the first place. Any return above that is a surplus that was never part of the threshold that made the venture worth undertaking. Investors who were content to share the normal return with the state will be no less content to share the surplus — the tax on that surplus does not diminish what they expected to receive, and it does not alter what they must receive to find the investment worthwhile.
Socrates: Just so. And notice what this means for the treasury’s full position. When the investment earns only its normal return, the state receives what a fair partner would receive. When it earns far more, the state takes an equal share of the surplus. When it loses — when the machine earns nothing — the state loses its co-invested share as well. It bears the risk; it shares the prize.
Thrasymachus: Mechanically, I cannot find a flaw in your chain of logic. But let me be sure I understand the scope of it. Does this neutrality hold regardless of how high the treasury raises its rate?
Socrates: It does, and this is the theorem’s most startling feature. A merchant facing a ninety percent tax rate under full expensing supplies only ten pieces of his own capital toward a one hundred piece machine, the remaining ninety pieces coming out of his tax reserve. If the machine yields its required return, the state takes ninety percent of that return — but the merchant’s ten pieces earned exactly what they needed to. The state has become the dominant partner. Yet the merchant’s decision at the margin is unchanged: the investment still clears its hurdle, because the hurdle was set against his ten pieces, not the state’s ninety.
Thrasymachus: Yet surely there must be some practical limit, Socrates. If the treasury raises its rate to ninety-nine parts in a hundred, my investor contributes only a single gold piece of his own toward the machine. His rate of return remains ten percent — yielding him a tenth of a gold piece at year’s end. But will any merchant truly devote his attention, hire scribes, bear the hazards of the venture, and navigate the law for a tenth of a gold piece?
Socrates: You have found the theorem’s practical boundary, and it is a real one. Every investment carries fixed burdens — the lawyer who drafts the contract, the accountant who keeps the books, the merchant’s own time and judgment — that the absolute return must cover regardless of the percentage rate. When the investor’s absolute stake shrinks toward nothing, these fixed costs consume his entire return however generous the deductions might be — the theorem preserves the rate of return, but fixed costs are absolute, not proportional. A principled treasury would recognize that its rate is bounded in practice by the minimum absolute return required to make participation worthwhile, a floor that varies by investment and by the fixed costs of the commerce in question. There is also a further constraint at extreme rates: the tax reserve itself has limits. A merchant accumulates his reserve gradually from prior earnings, and a very large co-investment may demand more than the reserve currently holds — a liquidity problem that, as we shall see, afflicts new enterprises with particular severity.
Thrasymachus: Then a treasury that wished to claim a very large share of capital returns could, in principle, do so without discouraging new investment, provided it honored the full expensing bargain, left the investor’s absolute return sufficient to cover the costs of participation, and ensured the state’s co-investment was actually delivered at the time the risk is taken?
Socrates: Provided it honored all of those conditions — and honored them immediately. For a merchant with an established and profitable business, the tax reserve provides the state’s share at the very moment of investment, automatically. But consider a young enterprise with no revenues and no reserve. The state has promised to share the cost through expensing, but if the young merchant has no taxable profits against which to apply the deduction today, the promise is hollow — he cannot withdraw coins that were never deposited. To preserve neutrality, the treasury must supply those coins through some other channel: an immediate cash refund, a transferable credit, or an equivalent instrument.
Thrasymachus: Surely the generosity of the treasury must have limits, Socrates! It is one thing to permit an established merchant to keep taxes he would otherwise have paid. Those coins were already in his purse, and the treasury merely declines to take them. But it is quite another thing for a young merchant with no profits, no reserve, and perhaps no proven judgment to demand that the treasury hand him forty pieces of gold for a venture whose prospects no one can know. The republic cannot become a venture-capital fund for every dreamer who sketches a machine on a tavern napkin.
Socrates: Your caution is entirely justified, Thrasymachus. If the treasury blindly handed out bags of gold up front, it would invite fraud, folly, and the wasting of the republic’s substance. No state could long survive it. But remember the nature of the bargain we established: the state only co-invests by honoring a cost-recovery rule on a legitimate transaction. If the young merchant has actually purchased the machine, then the transaction has already occurred. The question is not whether the treasury should choose the investment, but whether it should honor the same cost-recovery rule it offers established merchants. Yet, if we agree that a direct cash handout is too dangerous a channel for the state’s share, how else might the treasury deliver its share of the cost without writing a blank check on day one?
Thrasymachus: Could the treasury simply record the deduction and allow the merchant to use it in a future year, once the machine has generated profits against which it can be applied?
Socrates: It could, and this is indeed the most common practical response. But recall our lesson from Part Two — a coin promised in the future is worth less than a coin in hand today. A simple carry-forward reintroduces in miniature the same time-value problem that made gradual depreciation an incomplete remedy. To fully preserve neutrality, the carried amount must grow each year at the appropriate rate, compensating for the cost of the delay. An interest-adjusted carry-forward achieves this; a simple carry-forward does not. Where the treasury provides none of these remedies — neither immediate refund, transferable credit, nor adjusted carry-forward — the neutrality breaks down, and the tax imposes a real burden on new ventures precisely where the economy most needs to encourage them.
Thrasymachus: Then the full expensing bargain runs in both directions. The merchant accepts the state as a partner. The state, in turn, must actually deliver its share at the time the risk is taken — not merely claim a share of the reward when the reward arrives.
Socrates: You have stated it exactly. The theorem is not merely a mathematical convenience for established firms. It is a description of what a neutral tax must do if it wishes to be neutral: share the risk when the risk is taken, not merely claim a portion of success after the fact. A state that does the first has earned the second. A state that claims a share of success without having shared the risk has abandoned the neutrality principle on which the entire argument rests. It is collecting a partner’s reward without having honored a partner’s obligation.
Thrasymachus: I came to this conversation certain that any tax on investment returns must diminish the will to invest. I leave it persuaded that this is not an inherent truth about all systems of capital taxation — it is a consequence of the method the treasury uses to measure taxable income. Tax the gross return before cost recovery, and you destroy investments that serve everyone: merchant, investors, blacksmith, worker, customer, and treasury alike — and you corrupt what remains, driving merchants toward increasingly risky ventures in search of the extraordinary returns the tax now demands. Allow gradual recovery through depreciation, and you reduce the wound without closing it — the distortion shrinks, but the selection effect persists. Allow immediate and full recovery, and the tax rate becomes — in the precise sense of the word — irrelevant to the marginal investment decision. The deadweight loss was not in the tax. It was in the accounting.
Socrates: That is the theorem, stated plainly. It was there in the ledger all along.
The effect of full-expensing, as demonstrated above, was first proved formally by E. Cary Brown in “Business-Income Taxation and Investment Incentives,” a chapter published in a 1948 festschrift: Income, employment and public policy; essays in honor of Alvin H. Hansen. Brown’s formal proof was expressed in present-value terms: he showed that under immediate expensing, the present value of the tax shield exactly offsets the present value of the government’s claim on future returns, producing complete neutrality with respect to marginal investment decisions at any tax rate. The dialogue above translates that result into the more intuitive language of proportional co-investment and risk-sharing — a restatement that is faithful to the theorem’s logic while making its mechanism visible to non-specialist readers. The theorem received little attention for decades before gaining renewed prominence in corporate tax reform debates. It achieved direct practical relevance in the United States when 100% bonus depreciation — full expensing of physical capital — was made permanent law in 2025. That neutrality, however, currently applies to most equipment and machinery but not to real property: commercial structures remain on 39-year depreciation schedules and residential structures on 27.5-year schedules, leaving the wound Part One describes partially open for real estate investment — a gap the theorem’s logic suggests has no principled justification.