"The political liberty of the subject," said Montesquieu, "is a tranquility of mind arising from the opinion each person has of his safety. In order to have this liberty, it is requisite the government be so constituted as one man needs not be afraid of another." The liberty of which Montesquieu spoke is directly promoted by apportioning power among political actors in a way that minimizes opportunities for those actors to determine conclusively the reach of their own powers. Montesquieu's constitution of liberty is the constitution that most plausibly establishes the rule of law. Montesquieu concluded that this constitution could best be achieved, and had been achieved in Britain, by assigning three fundamentally different governmental activities to different actors. He was wrong. His mistaken conclusion rested on two errors. The first of these was theoretical; the second, both empirical and theoretical. First, Montesquieu's analysis was informed by the early eighteenth-century orthodoxy that no sovereign power could viably be divided. Montesquieu rightly saw that liberty from the arbitrary exercise of power would be served by apportioning power among multiple actors, but he thought the apportionment sustainable only if along essentialist lines. Lawmaking could be separated from law-executing, but neither of those kinds of power could durably be divided internally. The extent to which actors participated in the exercise of more than one kind of power Montesquieu viewed as a protective qualification to a primary essentialist separation. He failed to see that involving multiple actors in every exercise of power, albeit by permitting actors' individual involvement in the exercise of more than one kind of power, is the true protection against arbitrariness. Checks and balances, not essentialist separation of activities, prevent actors from conclusively determining the reach of their own powers. The critical liberty-promoting criterion for separation is not whether powers differ in kind, but whether apportionment will prevent actors from conclusively determining the reach of their own powers. Second, Montesquieu did not appreciate the nature of the English common law and the mechanism that its doctrine of precedent established for authoritative judicial exposition of existing law. That empirical error caused him to distinguish and trivialize the English judicial function as merely the ad hoc determination of disputed facts. Consequently, Montesquieu failed to recognize the lawmaking character of English judicial exposition. This essay analyzes implications of Montesquieu's mistakes for modern claims, both in Britain and in the United States, that liberty and the rule of law are promoted by separating power in certain contexts. In particular, this essay questions the British Government's recent claim that the values underlying separation of powers theory call for removing ultimate appellate jurisdiction from the House of Lords. It also traces Montesquieu's influence on the American founders' attempt to separate power along essentialist lines, and considers some sub-optimal consequences of that attempt, including the nondelegation quandary and the emergence of an unchecked judicial lawmaker.
