A Regulative principle (n.) is, in Kant's sense, a subjective rule of thought, not a quality of the object; mechanism and teleology are both such principles and so, Jung argued, need not contradict.
A Regulative principle (n.) governs how unity of experience is to arise from perceptions, without constituting the objects themselves.
A Regulative principle (n.) of reason is not an axiom about the world but a standing order to the inquirer: keep going back through the conditions, and never be allowed to stop at something unconditioned.
A Regulative principle (n.) cannot say what the object is, only how the regress must be carried on to reach the complete concept of the object — otherwise it would be constitutive, which pure reason can never be.
The Regulative principle (n.) aims at a focus imaginarius, the point outside all possible experience at which the lines of the understanding's rules converge — like objects seen behind a mirror, an illusion indispensable if we want to see what lies far behind our backs.
A Regulative principle (n.) becomes constitutive the moment it touches action: the same principle that determines nothing about things determines everything about what we do.