Under what conditions is capital structure irrelevant to firm value according to Modigliani-Miller, and why do these conditions matter?

Modigliani-Miller (MM) Proposition I states that in a frictionless market, the total value of a firm is independent of its capital structure. The firm's value is determined solely by the cash flows from its assets, not by how those cash flows are divided between debt and equity holders.\n\nThe Irrelevance Conditions:\n\n1. No taxes: No corporate or personal income taxes\n2. No bankruptcy costs: Financial distress imposes no costs on the firm\n3. No agency costs: Managers act perfectly in shareholders' interests; no bondholder-stockholder conflicts\n4. Symmetric information: Managers and investors have the same information\n5. No transaction costs: Issuing and trading securities is costless\n6. Individuals can borrow at the same rate as corporations: Homemade leverage replicates corporate leverage\n\nThe Intuition:\n\nImagine a pizza. Whether you cut it into 6 slices or 8 slices, you have the same total amount of pizza. MM says the same about firm value: whether you divide cash flows into debt and equity in any proportion, the total value remains the same.\n\nIf MM were violated in a frictionless market, arbitrageurs could profit by buying the cheaper firm and selling the expensive one. Specifically, investors could undo any corporate leverage decision by adjusting their personal borrowing, ensuring that identical cash flow streams command identical valuations.\n\nWorked Example:\n\nEvershaw Manufacturing generates $10M in annual operating income. In a world without taxes or frictions:\n\n| Structure | Debt | Equity Value | Firm Value |\n|---|---|---|---|\n| All equity | $0 | $100M | $100M |\n| 40% debt at 6% | $40M | $60M | $100M |\n| 70% debt at 6% | $70M | $30M | $100M |\n\nEquity holders in the levered firm earn higher returns (due to leverage amplification) but face proportionally higher risk. The risk-return trade-off exactly offsets, leaving firm value unchanged.\n\nWhy It Matters -- Relaxing Each Condition:\n\n| Condition Relaxed | Effect on Capital Structure |\n|---|---|\n| Introduce corporate taxes | Debt creates tax shields; optimal to use more debt |\n| Introduce bankruptcy costs | Too much debt risks costly distress; optimal debt is finite |\n| Introduce agency costs | Debt disciplines managers but creates asset substitution risk |\n| Information asymmetry | Pecking order: internal funds preferred over external |\n| Transaction costs | Firms avoid frequent capital structure adjustments |\n\nEach real-world friction creates a reason why capital structure matters, and the modern theories of capital structure (trade-off theory, pecking order, market timing) are essentially MM plus specific frictions.\n\nExam Significance:\nMM is the starting point for all CFA corporate finance capital structure questions. Understand the conditions, then systematically introduce each friction to explain observed behavior.\n\nDeepen your corporate finance knowledge in our CFA Corporate Finance course.