ent that Hume levels against those that see reason alone as able to motivate is his 'is and ought' argument. On the rationalist system, virtue and vice are discovered by reason alone through facts or relations. Whereas with the hypothetical imperative it is relatively simple to see why someone acts, as they act in order to achieve some goal (ie. If you want x then you ought to do y), it does not follow from a fact ('is' statement) that you ought to pursue a certain course of action. As Hume points out "No imperative conclusion can be validly drawn from a set of premises which does not contain at least one imperativeIn this logical ruleis to be found the bases of Hume's celebrated observation on the impossibility of deducing an 'ought'-proposition from a series of 'is'-propositions" (R.M. Hare 'The Language of Morals').One problem with the Humean notion of morality though is that if morality is based on an individual's sentiment, how can we have any absolute, universal notion of morality? Won't every individual simply have his/her own morality?Hume replies that underneath each rational being's own morality, there will be a deeper universal morality in basic notions such as justice, etc. However, I couldn't find any convincing justification of this idea.So, how does Kant answer the objection that a categorical imperative will never alone lead to action? He cannot use examples of reason alone motivating, as we can never tell that subconsciously or otherwise another factor isn't in fact involved. He therefore will have to prove the possibility of the categorical imperative being applied in reality a priori. He argues in the third section of the 'Grounding for the Metaphysics of Morals' that they key to moral action is freedom of the will. He still though doesn't explain how a categorical imperative can motivate.His answer is in fact fairly disappointing. He argues that we all take a great deal of interest in the moral law, and tha...
