Aristotle and Immanuel Kant were two renowned thinkers in drastically different time periods. However, they came to some strikingly similar ideas about philosophy and morality. In the end, their viewpoints parted ways substantially, but some of their core principles are clearly in the same vein.

For instance, both Kant and Aristotle believed that an action undertaken with a good and moral cause in mind was a moral action. Even if the outcome was negative unintentionally, the intent was moral, and therefore the action was as well. Additionally, they believed that there were some actions that were inherently evil and should be avoided at all costs.

Beyond that, however, the two had some differences of opinion. The two men had a difference in opinion when considering the results of actions. Kant believed that the result should never be considered—it was only the intent that mattered. However, Aristotle believed that if you chose to take an action and knew that there was an action that could result in a better solution, you were being immoral by choosing the initial action. Additionally, Kant believed that the most moral thing in life was to do your assigned duties—follow the letter of the law and whatever is prescribed to you. For Aristotle, he believed that the best action in life was to strive for the goodwill of others. In many ways this is just a semantic difference, but there are subtle nuances that separate the two.

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. 

Similarities

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. 

Differences

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.  

There are several similarities and differences in the ethical theories of Aristotle and Kant as will be highlighted below.

Similarities

1. Both believe that morality is achieved by actions which seek the highest good
2. Both believe that reason should be employed in determining actions
3. Both believe that some actions are intrinsically evil

Differences

1. According to Kant, consequences of an action are irrelevant in determining whether an action is moral or not where as Aristotle asserts that we can face consequences of voluntary actions
2. For Aristotle, the highest good is happiness which is achieved through virtuous actions whereas Kant believes that good will is the only virtue and is achieved through duty
3. For Kant, morality is defined by the performance of one’s duties compared to Aristotle who asserts that morality is determined by virtuous actions

Aristotle and Immanuel Kant are similar in their aapproaches to ethics in so far as they both admire reason or rationality. Also, their ethics, although admitting of the existence of a deity, are, to a large degree, secular, in the sense that though a deity is posited in both, divine revelation or Scriptural texts are not significant starting points for their ethical theories.

The first main difference is that Aristotle creates a form of virtue ethics in which the highest goal is eudaimonia (living well or thriving). Kant, on the other hand, creates a deontological ethics in which the highest good is acting according to a sense of duty alone and following absolute principles.