In the search for the supreme good, he assumes that it has three characteristics that stand out regardless of what the supreme good is, these are always the same. It must be desirable in itself. Aristotle thinks that the way a human being can be happy in life is to successfully lead a life full of rational activity, this is because rationality is the defining human characteristic, but he also believes that it should be in accordance with virtue in order to have a healthy soul. The Aristotelian system involves the concept of "natural kinds", Aristotle found this idea attractive. It consists of Species, Genus and Differentia, these ideas separate living beings into their natural species, to people it would be said that the animal is out of genus. Human beings are out of species and the difference, which is what makes us different, is our ability to reason and be rational. Because of who humans are and our ability to be rational, we are unable to live like any other type of animal because to be happy we must actualize and use our ability to be rational through activity. Having divided the soul into three parts, Aristotle could then determine which part happiness was associated with. He came to the conclusion that since happiness has to do with actions performed, it must come from the rational