Existentialism is probably my favorite bad philosophy. So much good stuff can be found in Existentialism that some might confuse me with one of them. The challenge of studying existentialism involves separating the good stuff from the bad stuff.
Part of the challenge of criticizing Existentialism has to do with the fact that Existentialism is not a consistent philosophical school. Most beliefs that are regarded as part of the philosophy are not universally accepted by all the Existentialist philosophers. I could explain why Kierkegaard's 3 stages of life experience are worthless outside of moral law, or why Nietzsche's Will to Power is seriously flawed, or why Sartre's concept of freedom can be disputed by Aristotle. But, other Existentialists already have.
The easiest way to tackle Existentialism, is to tackle its one and only axiom: existence precedes essence. The primary belief in layman's terms is that there is no such thing as human nature. If you look at the grand view of human diversity, it is difficult to find any commonalities that are universal to every human being. It is the belief of the Existentialists that you never will.
If the Existentialists are right, then there can never be any universal morals. Concepts of superior and inferior humans are justified. The belief that there is no human nature was a primary belief of both Karl Marx and Adolf Hitler. Whatever society decides is moral must be valid.
Are the Existentialists right? No*.
Mortimer J. Adler, in his book Ten Philosophical Mistakes, devotes a whole chapter as to why the Existentialists concept of human nature is flawed. He writes:
Looked at one way, the denial of human nature is correct. The members of the human species do not have a specific or common nature in the same sense that the members of other animal species do. ... But to concede [this] is not to admit that they have no specific nature whatsoever. An alternative remains open; namely, that the members of the human species all have the same nature in quite a different sense. ...
The answer can be given in a single word: potentialities. Human nature is constituted by all the species specific properties common to all members of the human species. ...
An innate potentiality is something determinable, not wholly determinate, and determinable in a wide variety of ways.
So, humans potential for speech can result in a wide variety of languages. The human potential for social structure, can result in a wide variety of cultures. The human potential for reason can result in a wide variety of belief systems.
By saying that human potential is a part of human nature, we are saying that cultural differences are not a result of superiority of some humans over other humans, but rather a result of something that makes us all human. All differences are a result of nurture rather than nature. As Adler states, "All the cultural and nurtured differences that separate one human subgroup from another are superficial as compared with the underlying common human nature that unites members of mankind."
The Ancient Greeks believed that the highest moral law was to live in conformity to our nature. The simplest interpretation of Plato's analogy of the cave (see my update The Darkened Theater if you are not familiar with the analogy) is that what philosophers are in search of is a common human nature to live by. To deny human nature is to deny human morality.
The denial of human nature is a major assumption of social scientists who study other cultures. They say that there are no common principles to be found in all cultures, therefore there are no common guides to live by. To continue Plato's analogy, the social scientists are just visiting different darkened theaters and stating that the movies are different. The Greeks themselves were the first to recognize the great differences in cultures. To them, what was important was to find the common good among the cultures and to reject the shortcomings of each culture. Ultimately, they searched for an ideal culture. To the modern social scientist, the Greek view is to view some cultures superior to other cultures, which modern eyes have rejected outright as wrong without any rational explanation. This, according to Allan Bloom, is the primary cause of the closing of the American mind. Cultural relativism leads to no culture at all, what the Existentialists call nihilism, which they consider a necessary thing, if not a good thing.
By rejecting the existential concept of human nature we can prove that many other Existentialist conclusions are also faulty. Especially moral subjectivism and cultural nihilism. But as I stated before, Existentialist thought is very diverse, and not all is dependent on the lack of human nature. There is still room for truth among the Existentialists.
A Guide to Existentialism is available.
Next: The Fatal Flaw of Humanism