These moral principles are the subject of what Kant terms formal philosophy, for formal philosophy is a discipline not grounded in the empirical realm. The Groundwork is Kant's attempt at establishing an a priori or rational foundation for morality. The supreme principle of morality which he concludes with is what he defines as the categorical imperative. Both physics and ethics have empirical and rational elements. Physics is the study of natural objects governed by natural laws.
Ethics is concerned with free objects which are governed by moral laws.
Laws cannot be considered absolute if they are grounded only in experience due to the contingency of the material realm. These principles are thus the a priori elements of the material sciences. Kant focuses upon the a priori foundation of ethics in an attempt to elucidate the supreme principle of morality. Kant begins by addressing the concept of a good will, arguing that only the good will is that which is good in itself. The will is good independent of its effects, laying the indicator of value solely upon intention.