(e.g., apples fall down because of gravity), objective rational laws necessitate rational actions. He thus believed that a perfectly rational being must also be perfectly moral, because a perfectly rational being subjectively finds it necessary to do what is rationally necessary. Because humans are not perfectly rational (they partly act by instinct), Kant believed that humans must conform their subjective will with objective rational laws, which he called conformity obligation. Kant argued that the objective law of reason is a priori, existing externally from rational being. Just as physical laws exist prior to physical beings, rational laws (morality) exist prior to rational beings. Therefore, according to Kant, rational morality is universal and cannot change depending on circumstance. Some have postulated a similarity between the first formulation of the Categorical Imperative and the Golden Rule. Kant himself criticized the Golden Rule as neither purely formal nor necessarily universally binding. Humanity as an end in itself Kant's second formulation of the Categorical Imperative is to treat humanity as an end in itself: Kant argued that rational beings can never be treated merely as means to ends; they must always also be treated as ends themselves, requiring that their own reasoned motives must be equally respected. This derives from Kant's claim that the sense of duty, the rational respect for law, motivates morality: it demands that we respect the rationality of all beings. A rational being cannot rationally consent to be used merely as a means to an end, so they must always be treated as an end. Kant justified this by arguing that moral obligation is a rational necessity: that which is rationally willed is morally right. Because all rational agents rationally will themselves to be an end and never merely a means, it is morally obligatory that they are treated as such. This does not mean that we can never treat a human as a means to an end, but that when we do, we also treat them as an end in themselves. Formula of autonomy Kant's formula of autonomy expresses the idea that an agent is obliged to follow the Categorical Imperative because of their rational will, rather than any outside influence. Kant believed that any moral law motivated by the desire to fulfill some other interest would deny the Categorical Imperative, leading him to argue that the moral law must only arise from a rational will. This principle requires