The meaninglessness of life, the absence of God, the loneliness of being a thinking individual — it sounds like the existentialists weren't the happiest group of folks, right? Not necessarily true. Read on to get an idea of what existentialism is all about.
Absurdity: What human beings encounter when they come into contact with the world. Absurdity is brought about because the human instinct to seek order and meaning is frustrated by the refusal of the world to be orderly or meaningful.
Anxiety: Kierkegaard said, "Anxiety is the dizziness of freedom." You feel anxiety because you recognize that you and you alone are responsible for your actions. This produces the two-sided feeling of simultaneous dread and exhilaration.
Alienation: The sense that you're a stranger in the world, or a stranger to yourself. Many aspects of existence can be alienating. One of the primary sources is absurdity. Ironically, the stories and systems developed by philosophy and religion to address that absurdity can be just as alienating.
Existence precedes essence: Sartre's phrase to describe the existential situation humans find themselves in. It refers to the fact that when you're born, you have no meaning, no purpose, no definition. Human beings exist first, and only later define themselves.
The Übermensch: The word Nietzsche uses to refer to his ideal human being. Literally "overman," the word reflects the importance in his philosophy of overcoming — overcoming traditional values, overcoming the herd mentality, and, most importantly, overcoming yourself. You overcome these things so that you might attain something greater. Nietzsche's Übermensch is an unconventional creator of values, a joyous free spirit, and one who embraces the earth instead of pining away for heaven.
The death of God: The death of the notion that belief in God alone, or belief in any religious or philosophical system, is sufficient to provide human beings with the meaning, purpose, and definition they crave. It's the recognition that, because no external system can provide you with the answers, you must take responsibility for providing them yourself.
Subjectivity: Your first-person perspective on the world, including the needs, desires, and emotions that accompany that perspective. The existentialists take this as a valid and important starting point for genuinely human endeavors. This can be contrasted with the scientific mindset, which always starts with objectivity — seeing people in impersonal, objective terms without emotion or appreciation for their individual point of view.