Miller and modigliani model
A financial theory stating that the market value of a firm is ascertained by its earning power and the risk of its underlying assets, and is independent of the way it selects to finance its investments or distribute dividends. Keep in mind, a firm can choose between three methods of financing: issuing shares, borrowing or spending profits (like opposed to dispersing them to shareholders in dividends). The theorem gets much more complexes, but the basic idea is that, under specific assumptions, it makes no dissimilarity whether a firm finances itself with debt or equity.