Aristotle wrote at least two different treatises on ethics, but most scholars believe his main work is his Nichomachean Ethics; named for his son Nicomachus. In his Nichomachean Ethics, Aristotle discusses the best kind of life a human should lead. He came to the conclusion that what humans should strive for is Happiness (Greek eudaimonia). A more accurate translation of the Greek word eudaimonia is fulfillment or human flourishment.
Aristotle said that a good human would perform his or her function just as other objects are considered good if they perform their function. For example, a good knife is a knife that cuts well. So what is the function of human beings? Using the knife in the example, a knife has a distinctive quality particular to it so that it can perform its function. This quality is sharpness. So, asked Aristotle, what is the distinctive property of humans which makes them different from animals? This, said Aristotle, is reason. We as humans can think about what we do, while animals just act on instinct. When we were younger, our parents made us do virtuous things, even if we didn’t want to. That in itself is not virtuous, but eventually we make a habit of it and then we desire to do virtuous things.
Virtues, said Aristotle, are means between vices. For example, generosity, a virtue, is a mean between prodigality and selfishness, vices. This, he says, is true for all virtues except Justice. He says this is true because there is no such thing as being too just.
Aristotle said that the good life consists of doing virtuous things and using our reason to think about our actions. Human beings should not act like giraffes or aardvarks who live by instinct, but should set about doing the proper function of a human: reason.