Existentialism is the philosophical concept that existence precedes essence. This is contrasted with the Platonic idea of the Forms, in which essence precedes existence. (According to Platonic ideas, there is a form of every tangible object, and the object itself is simply an imperfect copy of the form. This idea can also be applied to intangible concepts such as that of justice.)
To put this in quasi-Christian terms, an existentialist does not think they were born with an immortal "soul" - if there is any such attribute to a person, it is developed throughout life.
The origins of modern existential thought are developed and explored in a thread of philosophical and literary works from Søren Kierkegaard (who famously declared that "Truth is Subjectivity") and Friedrich Nietzsche (who famously declared that "God is dead"), through Martin Heidegger and Karl Jaspers, to the French writers Jean-Paul Sartre, Albert Camus, and Simone de Beauvoir, and playwrights Eugène Ionesco and Samuel Beckett (and Sartre again).
 In the 20th century
Existentialism peaked in popularity, both in serious philosophical thought and popular culture influence, from the 1950s to the 1970s. In terms of popular culture influence, a lot of novels and films during the period formed their premises around what the writers thought existentialism was about:
- Life is meaningless
- You create your own reality
- We are doomed to be free
- You must find a way to cope with your existence
- Being and experiencing are preferable to following a moral code or some purpose in life
- Human potential is unlimited even though there is no ultimate meaning to it
These lines of thought make existentialism somewhat related to (although not the same thing as) nihilism and egoism. Existentialism in some ways was a philosophy ready-made for the post-World War II era, during which people struggled to make sense of the evils that had just occurred and tended to hold grand purposes in life in disdain (seen as having led, among other things, to communism and fascism). After the 1970s, academic philosophers moved away from existentialism into other influences such as postmodernism.
 Existential crisis
A key concept in existentialist philosophy is the notion of overcoming an existential crisis, that is, a feeling of helplessness or desperation in the face of life's great questions. The idea of a crisis has largely been replaced by the concept of depression in modern medicine, although the two are distinct.
A crisis may be brought on by a number of factors, most notably:
- A full recognition of one's mortality, and a realization that one is going to die
- Witnessing great acts of suffering or evil, that dispel notions that the world is a good place
- Being alone or isolated, either physically or emotionally
- A questioning of all the values and norms that you've automatically followed throughout your life
- A feeling of total insignificance in the face of the enormity of the cosmos
 Friedrich Nietzsche
Nietzsche's works are peppered with existentialist thought, Twilight of the Idols, Daybreak and Ecce Homo being the most notable examples. In them, he promoted a concept known as self-creation, which is basically changing parts of yourself in order to create a more satisfying life, thus dealing with any existential angst you may have.
The process involves accepting the life and personality that you have, and working to make sense of them or better them. If you have a tendency for jealousy, or are quick to anger, these may be making your life problematic and existentially unbearable. Nietzsche thought tendencies and traits like these could be pruned out, and uses a gardening metaphor to make this clear:
“”One can dispose of one's drives like a gardener and … cultivate the shoots of anger, pity, curiosity, vanity as productively and profitably as a beautiful fruit tree on a trellis … all of this we are at liberty to do: but how many know we are at liberty to do it? (Daybreak 560)
By making your garden (i.e your personality) look more beautiful, the threat of an existential crisis is lessened. The theory of self-creation is a key concept in existentialism because it's an example of a solution to existential threats that don't involve acceptance of nihilism.
 Further reading
- Irrational Man: A Study in Existential Philosophy, (1958), Barrett, William, Doubleday (Anchor paperback 1962), New York. ISBN-10: 0385031386 - A good overview of the history of existential thought.
- Existentialism from Dostoevsky to Sartre, (1975), Walter Kaufmann (editor), Plume/Meridian. ISBN-10: 0452009308 - by the man who brought us a great series of translations of Nietzsche's works.