There are some staunch and subtle difference between the two men. Essentially, both men regarded morality from the perspective that the ends don't necessarily negate the means. Likewise, both men believed in logically deciphering what was righteous and moral. But the basis for truly understanding them lies in understanding their differences.
1. Both men argued that an act was moral is if were undertaken with a moral cause in mind. More plainly stated, in most situations, the morality of an individual is judged by his action, not by the outcome of that action.
2. Both men believed that logic was the only way to understand the moral world. They argued that emotions alone were too subjective to be useful in making moral claims.
3. Both men argued and understood that there were some actions that were intrinsically evil, and should never be taken.
1. According to Kant, the ends were never to be considered if an action were morally undertaken. To that end, regardless of how the choice to act turned out, the act would always be moral, if it began as a moral act. For Aristotle, this belief was mostly true as well. The fundamental difference between the two men is that Aristotle argued that if the ends were considered, found to be totally unjust, and no other alternative was present, the action would still be morally righteous if it were taken. However, if the ends were considered, found to be unmet, and a better alternative were present, but it were not taken, the action could be ruled immoral! based on the outcome. He argued this because the choice to do what was ill-suited for the greatest good was never a moral decision.
2. Kant's theories are argued from a deontological perspective, in that they are not situational. Kant believed that morality was ruled by laws and codes of actions. Aristotle argued that morality was ruled as a variance between extremes. His theories were more teleological, because they could be situational.
3. Aristotle argued that a person was virtuous if he upheld goodwill for the greatest good and made choices based on that ideal. For Arostotle, virtue was measurable. Kant believed that this was a false construct, because goodwill was unquantifiable, and was determined by law so it never changed.