The main idea behind Hume's moral philosophy is the difference between morality as a function of reason from morality as a matter of sentiment and passion. He believes that our morals are based on the way we feel along with the way others feel and our understanding of each of these. Reason and sentiment are said to occur in all moral decisions. Without feelings no decisions can be determined as moral or immoral. He found it impossible to find the difference between an "ought" and an "is." If feelings determine morals, then every individual's idea of what is right and what is wrong will be different or could even be completely opposite. If you were raised to think speeding is wrong and the community you live in does not speed, then you will believe speeding is immoral. If you grow up in the opposite atmosphere then speeding will be the furthest thing from immoral. .
Kant asks, what if feelings disagree? For example, what I believe to be right is the opposite from what one of my classmates believes based on what each of our families has taught us. My parents believe stealing is wrong and immoral, but their parents taught them how to steal and believe it is completely moral and okay. In this case, which instance is moral and which instance is not? Kant believes morality is based completely on reason. Reason, says Kant, has a practical side, which can tell us what and how to do things. If morality is based on feelings, then the thief would be right in his environment, and I would be right in mine. But morality cannot be different in that way. Morals do not depend on circumstances, society, or feelings. Morals have to be universal; they cannot change from society to society. One person cannot believe something to be immoral that another has deemed to be moral because if they were to ever have to cross paths chaos would occur. According to Kant, each person's actions should be consistent with the idea of humanity.