Being and Nothingness

Until the late 19th century, most philosophers accepted the idea of essences set forth by Aristotle. Essences are the inherent properties that make something what it is; for example, the ink of a pen is a part of its essence. Without ink, a student doing his homework may only be holding a useless stick. This means that humans also have an essence, a predetermined purpose set forth by God that defines them as a species. Aristotle proposed that all creatures and things acted in accordance with their essence; the meaning of life was viewed as discovering and adhering to this essence.

In the 19th century, Nietzsche introduced the world to nihilism, the theory that life is meaningless, while Kierkegaard—the father of existentialism—emphasized the role of individuality, particularly within the realm of Christianity. Jean-Paul Sartre was profoundly influenced by philosophers like Nietzsche and Kierkegaard, and he developed his own theories about essences that shifted the way many philosophers thought about the meaning of life. Sartre saw a fundamental difference between humans and other creatures, proposing an approach to the human condition that embraced both the meaninglessness of life and the role of individuality in approaching this problem of existence.