Acting on a Maxim, Reason, Causality

Because Kant's concept of Practical Reason is verbal, a more instructive term that captures both of its innovative features is Prescriptive Reason.  Likewise, Theoretical Reason is more accurately Descriptive Reason.  Now, the foundational concept of his Moral doctrine is not his Fundamental Principle of Pure Practical Reason, but the component that it presupposes, and that Kant introduces with no preparation--Acting on a Maxim.  A Maxim is a verbal formulation of a Means-End relation, and, hence, is an incorporation of a Cause-Effect relation into behavior.  It is thus subject to two of Hume's criticisms--that the Causal connection is not Necessary, and that the End is not Rational.  However, and Kant seems to not consider it, Acting on a Maxim is outside of both of those criticisms--1. The Causality involved in Acting on a Maxim is Formal, i. e. a Maxim unifies a sequence of motions; and 2. The Reason involved is Technical, i. e. an expression of Know-How.  Now, a Kantian Maxim is hardly a unique example of Prescriptive Reason--any set of instructions, directions, recipes, etc. all exemplify it, as does Wittgenstein's Following a Rule.  But a reason why so common a phenomenon has received so little specialized Philosophical attention may be because it includes an irreducible physical component, and much of the history of Philosophy has been hostile to Corporeality.