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From the late 1950s to the early 1970s the field of finance changed fundamentally. A reader of the Journal of Finance in the early 1950s would find a field that was mostly descriptive. After the early 1970s the field had become a science. Merton Miller was at the centre of that transformation. His work started it in 1958. For the rest of his life he was at the heart of modern finance. (Grundy 2001, provides a complete list of Merton Miller’s publications.)

After obtaining a Ph.D. in economics from Johns Hopkins University in 1952 and a brief stay at the London School of Economics, he joined the Graduate School of Industrial Administration at what was then known as Carnegie Tech. As an assistant and associate professor there, he made the contributions to the theory of corporate finance with Franco Modigliani, another faculty member, that made him famous. He joined the University of Chicago in 1961. From Chicago he exerted a huge influence on finance which lasted until he died in 2000. Merton Miller’s research had a prodigious impact – he made major contributions in monetary economics, operations research, derivatives pricing, and asset pricing, as well as his seminal contributions in corporate finance – but his influence went far beyond the contributions of his papers. He mentored countless Chicago graduate students and faculty members from Chicago and throughout the profession. At times he played the role of the nurturing patriarch, while at other times he used his wit and intellect to keep people on the straight and narrow path of solid economic thinking. From ‘his’ seat on the left of the speaker in the Rosenwald seminar room, often in a worn-out sweater, he changed the course of numerous papers. Sometimes his intervention went further – for example, he was instrumental in persuading the Journal of Political Economy to publish the paper by Black and Scholes that is the foundation of option pricing theory. When he ventured outside of the University of Chicago, he often did so to be ‘an activist supporter of free-market solutions to economic problems’, as he stated in a brief Nobel autobiography (1991a). He knew how to make his case – he was not the son of an attorney, a Harvard graduate also, for nothing – and had a well-deserved reputation for unparalleled eloquence in the finance profession.

The Irrelevance Propositions and the Role of Arbitrage

Merton Miller earned a Nobel Prize in economics in 1990 for his ‘fundamental contributions to the theory of corporate finance’ (Franco Modigliani already had a Nobel Prize by then for his life cycle theory of saving). Just about every MBA in the world has learned the famous MM irrelevance propositions he developed with Franco Modigliani. (One paper had Modigliani’s name first and the other had Miller’s name first, so I will proceed using the moniker MM to represent the team.) The two key MM irrelevance propositions are developed in a world with perfect markets, so that there are no frictions. In particular, there are no transactions costs or taxes, and no costs are incurred to induce managers to maximize the value of the firm.

The first irrelevance proposition, Proposition I in the paper titled ‘The Cost of Capital, Corporation Finance and the Theory of Investment’ published in the American Economic Review (1958, p. 268) states that ‘the market value of any firm is independent of its capital structure and is given by capitalizing its expected return at the rate. ... appropriate to its class’. The second irrelevance proposition concludes that ‘given a firm’s investment policy, the dividend payout it chooses to follow will affect neither the current price of its shares nor the total return to its shareholders’ (1961, p. 414). In other words, in perfect markets neither capital structure choices nor dividend policy decisions matter. Since then, corporate finance has refined these results and built theories based on the existence of market imperfections.

If we had to remember one thing about Merton Miller’s contributions to finance, what should it be? It would not be the irrelevance propositions themselves. Rather, it would be the way the irrelevance propositions were proved (for a more complete analysis, see Stulz 2000). The approach used to prove these propositions is central to the thinking of practitioners of modern finance. It has spawned many seminal contributions to the field. The method used to prove Proposition I is the method of arbitrage. MM did not invent arbitrage, but made it the foundation of modern finance. MM assume that financial markets are perfect and then show that

if Proposition I did not hold, an investor could buy and sell stocks and bonds in such a way as to exchange one income stream for another stream, identical in all relevant respects but selling at a lower price. The exchange would therefore be advantageous to the investor quite independently of his attitudes toward risk. As investors exploit these arbitrage opportunities, the value of the overpriced shares will fall and that of the underpriced shares will rise, thereby tending to eliminate the discrepancy between the market values of the firms. (1958, p. 269)

The arbitrage mechanism is how Merton Miller thought about finance phenomena. Results that would lead to arbitrage opportunities could not possibly be important because market forces would step in to make prices right. However, in his thinking arbitrage was never limited to existing financial instruments and institutions. For him, arbitrage opportunities that exist in the real world will eventually disappear because, when needed, financial innovations will occur that will prevent these opportunities from persisting.

Though arbitrage arguments are now pervasive throughout finance and, more generally, economics, the more immediate and direct impact of the arbitrage proof of Proposition I was to provide the foundation for modern corporate finance because it specifies sufficient conditions for leverage not to matter. Because of the proof, we know that, if financial markets are perfect, the value of a firm does not depend on its leverage. As a result, practitioners and academics alike know that, if leverage affects value, it must be that one or more of the assumptions required by the arbitrage proof do not hold.

In their papers MM eliminated once and for all the argument that leverage is costly simply because it increases the interest rate the corporation pays for its debt. As leverage increases in a world of perfect markets, the coupon paid on debt increases, but that is because bondholders bear more risk and must be compensated for this additional risk. This will happen even though the firm’s cash flows are unaffected by the additional leverage. Hence, as Merton Miller pointed out in his Nobel lecture (Miller 1991c), the increase in the risk of debt has no social costs because the firm’s total risk is unaffected by the change in leverage.

Beyond the Rrrelevance Propositions

With corporate income taxes, the cost of debt for the firm is the cost after taxes since interest paid on debt is tax deductible at the corporate level. If the only departure from the assumptions leading to Proposition I were a tax subsidy to corporate debt, one would expect firms to maximize the value of that subsidy and therefore have extremely high leverage. Empirically, however, leverage is not extreme. To make sense of the limited levels of leverage in the presence of what appeared to be a large tax subsidy for debt, finance had either to relax other assumptions leading to Proposition I or to conclude that the subsidy was illusory. Initially, the route chosen by finance was to take into account bankruptcy costs. Bankruptcy costs occur because contracting is costly – firms that default on their debt contracts cannot be costlessly reorganized. In the presence of bankruptcy costs and tax subsidy to debt, each firm has an optimal debt level such that the increase in the present value of expected bankruptcy costs resulting from an additional dollar of debt equals the present value of the expected tax subsidy from that additional dollar of debt.

Merton Miller always doubted that expected bankruptcy costs could be large enough to explain why firms did not take greater advantage of the tax subsidy of debt. His assessment of the evidence on bankruptcy and financial distress costs was that ‘neither empirical research nor simple common sense could convincingly sustain these presumed costs of bankruptcy as a sufficient, or even as a major, reason for the failure of so many large, well-managed US corporations to pick up what seemed to be billions upon billions of dollars of potential tax subsidies’ (1991b, p. 274). This assessment led him to one of his most memorable statements, namely, that ‘the supposed trade-off between tax gains and bankruptcy costs looks suspiciously like the recipe for the fabled horse-and-rabbit stew – one horse and one rabbit’ (1976, p. 264).

Since direct bankruptcy costs could not explain why firms were not taking advantage of the apparent tax subsidy of debt, the field of finance turned to other explanations for low leverage based on contracting costs. Jensen and Meckling (1976) showed that, as leverage increases, shareholders have incentives to take advantage of bondholders by undertaking highly risky projects with high payoffs to shareholders in some states even though such projects have a negative net present value. The bondholder–shareholder conflict identified by Jensen and Meckling makes debt more costly because firms either behave inefficiently as a result of leverage or spend real resources to convince bondholders that they will not take advantage of them. A large literature emphasizing contracting costs has developed over time.

Merton Miller always had doubts that the bondholder–shareholder conflict could explain why firms did not take greater advantage of the tax shield of debt. Not surprisingly, his scepticism stemmed from the role of arbitrage in his thinking. If the tax shield of debt was so large, why was it that investment bankers would not devise solutions that would enable firms to take advantage of this tax shield and overcome the agency costs of debt through clever contracting? As always, he viewed no finance problem as solved unless he could find a solution that would not provide clever arbitrageurs with profit opportunities.

In 1976, in his address as President of the American Finance Association, Merton Miller revisited the issue of the impact of corporate taxation on the MM irrelevance propositions in a classic paper titled ‘Debt and Taxes’. This paper shows perhaps better than any of his other papers how he could use arbitrage arguments to change the way finance academics and practitioners understood how the world works. In that paper he pointed out that the tax advantage of corporate debt might be mostly if not completely illusory. Because interest on corporate debt is taxed as income to the bondholder, the interest paid must be sufficiently high to ensure that the after-tax income from holding corporate bonds is attractive relative to the income from equity which, when it accrues as capital gains, is taxed at a lower effective rate. While corporate interest payments generate tax deductions, personal taxes on interest income are higher than on capital gains, and so the before-tax cost of capital on debt must be higher than on equity to induce investors to hold debt. In his paper Merton Miller showed that under specific conditions the only feasible equilibrium is the one in which the after-tax cost of debt equals the after-tax cost of equity. When this equilibrium obtains, Proposition I holds in the presence of taxes, and no firm has a financial incentive to alter its mix of debt and equity even though interest payments on debt are tax deductible. ‘Debt and Taxes’ demonstrated that the perfect-markets assumptions are sufficient, but not necessary, conditions for leverage to be irrelevant. Showing that the assumptions required for Proposition I do not hold is not enough to conclude that leverage matters; rather it must also be the case that clever arbitrageurs cannot profit from the situation.

The Legacy

With the contributions to the field of finance that I have described, Merton Miller provided a way to think about financial phenomena that remains at the core of all major theoretical developments in the field. Throughout his life, Merton Miller used arbitrage reasoning to organize his thoughts about important phenomena. His first publication appeared in the 1948 American Economic Review. In 1990, he published a paper in the Journal of Finance (co-authored with David Hsieh) that analysed the impact on stock prices of changes in margin requirements. That paper was awarded a Smith–Breeden prize for best paper in the Journal of Finance. At the time, Merton Miller was thrilled because he had published refereed papers in top journals in five different decades. He never stopped wanting to write papers that merited publication in top journals. Three days before his death he was preparing a paper for submission. Throughout his life he was first, last, and foremost a scholar.

See Also

Selected works

  • 1948. (With R. Musgrave.) Built-in flexibility. American Economic Review 38, 122–128.

  • 1958. (With F. Modigliani.) The cost of capital, corporation finance and the theory of investment. American Economic Review 48, 261–297.

  • 1961. (With F. Modigliani.) Dividend policy, growth, and the valuation of shares. Journal of Business 34, 411–433.

  • 1976. Debt and taxes. Journal of Finance 32, 261–275.

  • 1990. (With D. Hsieh.) Margin regulation and stock market volatility. Journal of Finance 45, 3–29.

  • 1991a. Autobiography. In Les Prix Nobel. The Nobel Prizes 1990, ed. Tore Frängsmyr. Stockholm: Nobel Foundation. Online. Available at http://nobelprize.org/nobel_prizes/economics/laureates/1990/miller-autobio.html. Accessed 28 June 2006.

  • 1991b. Financial Innovations and Market Volatility. Cambridge, MA/Oxford, UK: Blackwell.

  • 1991c. Leverage. Journal of Finance 46, 479–488.