ences for two reasons. First, any empirical knowledge must be preceded by metaphysics. For example, when an apple falls to the ground it does so because of an a priori law of gravitation. This law, based in metaphysics of nature, exists independent of and prior to the phenomena of the apple's fall. Similarly, Kant argues practical anthropology as the empirical branch of ethics necessitates a metaphysics of morals to precede it. Second, metaphysics of morals is necessary as a condition of preventing morals from being tainted by human inclinations and interests. Kant writes that in the absence of an a priori law of morality morals become "liable to all kinds of corruption". Metaphysics of morals embraces a universal moral law which cannot be molded to suit specific interests.
             Having outlined what it means for moral philosophy to be pure and why purity is necessary, Kant goes on to identify the form this metaphysics of morals takes. Kant argues that the moral law that is revealed by pure reason is the categorical imperative, a universally applicable command of reason. The categorical imperative may be articulated through three interrelated formulations. The first is universality: "Act only according to that maxim by which you can at the same time will that it should become universal law." This formulation serves to prohibit actions that contradict their ends by exposing that contradiction through application to a universal scale. For example, cutting in line is not a moral action because if everyone were to do so it would negate the concept of a line. Human dignity is the second formulation. This commands that you act in such a way that you treat humanity always at the same time as an end and never simply as a means. The final formulation, autonomy, states that one should act on maxims "such as the will can thereby regard itself at the same time t
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