The rationale of the separation of powers is often elided with the rationale of checks and balances and with the rationale of the dispersal of power generally in a constitutional system. This Essay, however, focuses resolutely on the functional separation of powers in what M.J.C. Vile called its “pure form.” Reexamining the theories of Locke, Montesquieu, and Madison, this Essay seeks to recover (amidst all their tautologies and evasions) a genuine case in favor of this principle. The Essay argues that the rationale of the separation of powers is closely related to that of the rule of law: it is partly a matter of the distinct integrity of each of the separated institutions—judiciary, legislature, and administration. But above all, it is a matter of articulated governance (as contrasted with compressed undifferentiated exercises of power).