In saying that "existence precedes essence" Sartre means to break away from Western metaphysics which held since Aristotle that the essence of things precedes their existence. Philosophy always thought that there is such as thing as "human nature" which is predetermined by either God or some other greater force. Even the view of humanity as resting on its capacity for rational thought, like in modern philosophy, things that we have an essence which is the basis of our existence.
For
Sartre, However, the idea that existence precedes essence means that the meaning
of who we are is not established by some pre-designed model or determined goal.
For Sartre this is a liberation of human essence which leaves it up to each and
every one of to choose our own essential meaning.
The action of existence determines essence
Sartre
recognizes that we our always bound by the preconditions of our existence. But
what is not predetermined is the meaning we give these circumstances and
especially the manner in which we interact with them. Reacting to the world
around us is for Sartre "a mirror of my freedom". He means that being
called to act upon the world is what makes us free, and that utilizing this
freedom is what gives meaning to who we are.
This does
not mean that we become who we are just by thinking it (like deciding that my
essence is actually that of a penguin). Our true essence comes from the way we
interact with the world around us. Our actions and choices are alone what define
us.
"we are condemned to be free"
Another famous quote by Sartre associated with "existence precedes essence" is "we are condemned to be free". In plane terms this argument means that we always have to choose and enact who we are, and that this burden is something we cannot unburden ourselves from.
The
assertion that existence precedes essence is the same as asserting that there
is no such predetermined essence found in humans and that an individual's
essence is defined by him or her through how he or she creates and lives his or
her life. As Sartre puts it in his work "Existentialism is Humanism":
"man first exists, meets himself, starts multiplying above the world - and
defines himself later."
Essence vs. Existence in Sartre’s Philosophy