The Metaphysics of Morals by Immanuel Kant Chapter 2 Page 103

Classification of all Principles of Morality which can be founded on the Conception of Heteronomy

Here as elsewhere human reason in its pure use, so long as it was not critically examined, has first tried all possible wrong ways before it succeeded in finding the one true way.

All principles which can be taken from this point of view are either empirical or rational. The former, drawn from the principle of happiness, are built on physical or moral feelings; the latter, drawn from the principle of perfection, are built either on the rational conception of perfection as a possible effect, or on that of an independent perfection (the will of God) as the determining cause of our will.

Empirical principles are wholly incapable of serving as a foundation for moral laws.