Epicureanism bases its ethics on a hedonistic set of values. In the most basic sense, Epicureans see pleasure as the purpose of life. As evidence for this, Epicureans say that nature seems to command us to avoid pain, and they point out that all animals try to avoid pain as much as possible. Epicureans had a very specific understanding of what the greatest pleasure was, and the focus of their ethics was on the avoidance of pain rather than seeking out pleasure.
Epicureanism divided pleasure into two broad categories: pleasures of the body and pleasures of the mind.
- Pleasures of the body: These pleasures involve sensations of the body, such as the act of eating delicious food or of being in a state of comfort free from pain, and exist only the present. One can only experience pleasures of the body in the moment, meaning they only exist as a person is experiencing them.
- Pleasures of the mind: These pleasures involve mental processes and states; feelings of joy, the lack of fear, and pleasant memories are all examples of pleasures of the mind. These pleasures of the mind do not only exist in the present, but also in the past and future, since memory of a past pleasant experience or the expectation of some potentially pleasing future can both be pleasurable experiences. Because of this, the pleasures of the mind are considered to be greater than those of the body.
The Epicureans further divided each of these types of pleasures into two categories: kinetic pleasure and katastematic pleasure.
- Kinetic pleasure: Kinetic pleasure describes the physical or mental pleasures that involve action or change. Eating delicious food, as well as fulfilling desires and removing pain, which is itself considered a pleasurable act, are all examples of kinetic pleasure in the physical sense. According to Epicurus, feelings of joy would be an example of mental kinetic pleasure.
- Katastematic pleasure: Katastematic pleasure describes the pleasure one feels while in a state without pain. Like kinetic pleasures, katastematic pleasures can also be physical, such as the state of not being thirsty, or mental, such as freedom from a state of fear. Complete physical katastematic pleasure is called aponia, and complete mental katastematic pleasure is called ataraxia.
From this understanding, Epicureans concluded that the greatest pleasure a person could reach was the complete removal of all pain, both physical and mental. The ultimate goal then of Epicurean ethics was to reach a state of aponia and ataraxia. In order to do this an Epicurean had to control their desires, because desire itself was seen as painful. Not only will controlling one's desires bring about aponia, as one will rarely suffer from not being physically satisfied, but controlling one's desires will also help to bring about ataraxia because one will not be anxious about becoming discomforted since one would have so few desires anyway.
Epicurus distinguishes three kinds of desires: the natural and necessary, the natural but not necessary, and those that are neither natural or necessary.
- Natural and necessary: These desires are limited desires that are innately present in all humans; it is part of human nature to have them. They are necessary for one of three reasons: necessary for happiness, necessary for freedom from bodily discomfort, and necessary for life. Clothing would belong to the first two categories, while something like food would belong to the third.
- Natural but not necessary: These desires are innate to humans, but they do not need to be fulfilled for their happiness or their survival. Wanting to eat delicious food when one is hungry is an example of a natural but not necessary desire. The main problem with these desires is that they fail to substantially increase a person's happiness, and at the same time require effort to obtain and are desired by people due to false beliefs that they are actually necessary. It is for this reason that they should be avoided.
- Not natural nor necessary: These desires are neither innate to humans nor required for happiness or health; indeed, they are also limitless and can never be fulfilled. Desires of wealth or fame would fall under this category, and such desires are to be avoided because they will ultimately only bring about discomfort.
If one follows only natural and necessary desires, then, according to Epicurus, one would be able to reach aponia and ataraxia and thereby the highest form of happiness.
Epicurus was also an early thinker to develop the notion of justice as a social contract. He defined justice as an agreement made by people not to harm each other. The point of living in a society with laws and punishments is to be protected from harm so that one is free to pursue happiness. Because of this, laws that do not contribute to promoting human happiness are not just. He gave his own unique version of the ethic of reciprocity, which differs from other formulations by emphasizing minimizing harm and maximizing happiness for oneself and others:
"It is impossible to live a pleasant life without living wisely and well and justly, and it is impossible to live wisely and well and justly without living a pleasant life."
- ("justly" meaning to prevent a "person from harming or being harmed by another")
Epicureanism incorporated a relatively full account of the social contract theory, and in part attempts to address issues with the society described in Plato's Republic. The social contract theory established by Epicureanism is based on mutual agreement, not divine decree.