A while ago, I suggested a scheme for the division of power between the executive and legislative branches (link) which involved two congressional bodies, an executive congress and a legislative congress. One of the goals of the scheme was to solidify the separation between policy making and policy enforcement. One question I failed to ask, though, was “what does it mean to have an optimal separation?” I don’t really doubt that the separation between legislative and executive powers is a good idea, but that I do not understand rigorously why the separation of executive and legislative powers is a good idea. To understand how much separation should exist and where powers should be separated for optimal operation, one must have a good understanding of why that separation is a good idea.
One could argue that separation of powers is largely to enforce the rule of law; putting distance between the creation of law and the execution of law means that the way for executive officers to maximize their power is to enforce the law broadly and therefore somewhat consistently over people and over time, but completely separating legislative and executive powers is not the only way to put distance between law making and law enforcement. Parliamentary systems, where the legislature elects the executive, have this feature when there are procedural restrains on the legislative body electing executive officers. For example, if executive officers are elected only at regular intervals there would be significant space between the formulation of law and execution of law. Part of the reason for separation must be this rule of law aspect, and part of it must also be the vague notion that separating power will cause the separate concentrations of power to limit each other and prevent tyranny. There has been at least one attempt to formalize this latter aspect, but I found it very unsatisfactory. Without a rigorous understanding of exactly what the purpose of the separation of powers is, it is impossible to determine what an “optimal” separation is, and that limits how much I can consider and compare different governmental structures.