ABSTRACTThis paper demonstrates that shareholder limited liability imposes a restriction on corporate borrowing and that failure to incorporate this restriction into the analysis yields the “reductio ad absurdum” argument against mean‐variance models of optimal capital structure. With corporate income taxes and costless bankruptcy, the firm's value is a monotonically increasing function of debt as long as the amount of debt does not exceed the upper limit imposed by shareholder limited liability. As a result, the introduction of costly bankruptcy into the mean‐variance framework is ju