According to Kant moral law must be known a priori, and must be able to be universally applied to all beings. Kant asserts that empirical explanations of morality may only be used as evidence to demonstrate that actions can be perceived as being moral, but are not to be used as devices for assessing the moral value of actions. “For every example of morality presented to me must be judged according to principles of morality to see if it is fit to serve as an original example.” (Kant Pg.20) Not to say that we cannot appeal to sentiment upon establishing that an action is moral, but it is the case that morality first must be established by universal moral standards. Kant feels that in order for morality to have proper influence, it must be able to be applied not only to humans, but all rational agents. Empirical methods of moral discovery can only account for human action and not that of any other rational agent. “Moral law is of such widespread significance that it must not hold merely for men but all rational beings...not merely on contingent conditions...but must be absolutely necessary.” (Kant Pg.20)
But what motivation does this offer us to be moral? If the principles of right and wrong exist a priori, and are universally applicable, are we simply meant to obey these principles for their own sake? If so, compliance may not be easy to achieve. Are these principles universally obligatory? If moral principles exist as a priori concepts how do we prove it? According to Hume if we examine these questions regarding morality empirically we find our motivation, as well as evidence of morality’s existence. “Morals excite the passions, and produce or prevent actions.” (Hume Pg.68) We experience the effects of morals in our sentiments, morally good actions elicit positive emotional responses and bad actions elicit negative emotional responses. It is our desire to feel positive, as opposed to negative emotions and thusly we comply with morality.
“For the pure thought of duty and of the moral law generally, unmixed with any extraneous addition of empirical inducements, has by reason alone an influence on the human heart more powerful than other incentives.” (Kant Pg.22) Pure moral laws provide their own motivation. According to Kant, morality can be known a priori by appealing to our transcendental reason. Our transcendental reason is not affected by empirical, causal contingencies and it is the source of our morality. This freedom to govern our own morality is the source of our motivation to appeal to reason. If we are to experience freedom, according to Kant we must appeal to these laws of reason that are of our own design.
Hume has a different perception of reason. “Reason is and ought only to be a slave to the passions.” According to Hume reason can only influence us in two ways. It can either excite our passions by granting us an understanding of relatable concepts with regards to problems we wish to solve, or by assessing the possible positive or negative outcomes of certain actions inspiring our emotions to motivate our actions in one way or another. Reason is otherwise an inactive principle that has no direct influence over our actions. Actions are completely motivated by the passions. “Reason is the discovery of truth or falsehood. Truth or falsehood consists in an agreement or disagreement either to real relations of ideas, or to real existence and matter of fact.”(Hume Pg.69) The purpose of reason is only directly applicable to these sorts of activities.
If it is the case that reason is a slave to the passions, then Kant would assert that we are not free, and...