Both Aristotle and Lucretius try to pin down what makes a human life truly human. Aristotle makes a distinction between the good, virtuous, human life and presumably the bad, unvirtuous, human life. For him, this distinction was necessary because he believed that the quality of human life determined the nature of the afterlife. A virtuous life was rewarded with a happy afterlife, and vice versa. Everybody wishes to be happy, and being happy typically includes things or experiences considered pleasurable. Descriptions of pleasurable and unpleasurable things involve an appeal to emotions. Being kissed by a girl is pleasurable, and may be associated with emotions of love or lust. Getting punched in the face is not pleasurable and may be associated with emotions of hatred, fear, anger, resentment. Emotions tend to affect our reaction to events that happen. Aristotle writes in the Rhetoric, "The emotions [pathe] are those things through which, by undergoing change, people come to differ in their judgements."(pg 121) The emotion of hatred felt after getting punched in the face, affects one's judgments in that they might punch back or never speak to that person again. In other words, the emotions affect the way one thinks. Because the emotions affect people in this way, Aristotle felt that in order to act rationally and virtuously, one must condition emotions to behave rationally. .
Aristotle believed that there were two elements to the Human soul, an irrational side and a rational side. The irrational side consisted of a vegetative and desiring part. The first represents the need for natural pleasures, like eating, reproduction, and eating. The second represents the need for social pleasures. We may desire good music and fine wine; however, these are not necessary for survival. The rational side of the soul, or the highest part, is that part that complies with, possesses and visualizes the rules of reason, or logic.