Paris, 1945. The war is over. Europe is in ruins. Millions of people are dead, and the old certainties — God, nation, progress, the natural order of things — have been shattered beyond repair. Into this wreckage steps a small, cross-eyed philosopher with thick glasses and an enormous pipe, and he delivers a lecture that will change the course of philosophy. His name is Jean-Paul Sartre, and the lecture is called 'Existentialism is a Humanism.' The hall is so packed that people faint from the heat. Sartre's central claim is both thrilling and terrifying: there is no God, no fixed human nature, no pre-written script for your life. You are radically, inescapably free. And that freedom is the heaviest burden you will ever carry.

To understand what Sartre meant, you need to grasp one of the most important phrases in all of modern philosophy: existence precedes essence. It sounds abstract, so let's unpack it with an example. Think about a paper knife — a letter opener. Before the craftsman makes it, the idea of the knife already exists in their mind. They know what it is for, what shape it must be, what its purpose is. The essence of the knife — its design, its function — comes before its existence as a physical object. For centuries, this is how people thought about human beings too. God, like the craftsman, had a design in mind before creating us. We were made for a purpose. Our essence — our nature, our soul, our telos — came before our existence. Sartre says: no. For human beings, it is the other way around. We exist first. We are thrown into the world with no pre-given nature, no divine blueprint, no fixed purpose. And only then, through our choices and actions, do we create what we are. Existence precedes essence.

What does it actually mean to say that existence precedes essence? It means that you are not born with a fixed identity. You are not, at your core, a coward or a hero, a good person or a bad one, a success or a failure. These are not things written into you before you arrived. They are things you become — through what you do, how you choose, how you act in the world. Sartre puts it bluntly: you are your choices. Not your intentions. Not your feelings. Not your potential. Your choices. The person who says 'I am, by nature, a shy person' is, in Sartre's view, making an excuse. Shyness is not a fixed essence. It is a pattern of choices that can, in principle, be chosen differently. This is an enormously liberating idea. But it is also, as Sartre freely admits, an enormously anxious one.

Sartre calls this anxiety 'anguish.' It is the vertigo of freedom — the dizzying realisation that nothing is decided for you, that every moment you must choose, and that you cannot escape responsibility for those choices by blaming your nature, your upbringing, your circumstances, or God. He uses a striking image: imagine you are standing at the edge of a cliff. You feel a strange pull — not a desire to jump, but a kind of dread at the fact that you could. Nothing is stopping you. The only thing between you and the edge is your own choice. That is anguish. It is the recognition that you are always, at every moment, the author of your own life — and that there is no one else to blame and nowhere to hide.

And this is where one of existentialism's most powerful concepts enters: bad faith. Bad faith is Sartre's term for the way people try to escape the burden of freedom by pretending they have no choice. We do this constantly, in a hundred different ways. The waiter who performs his role so perfectly, so mechanically, that he seems to be playing at being a waiter rather than simply being a human being who happens to be serving tables. He has made his identity into a fixed thing, a role, an essence — and in doing so, he has denied his own freedom. Or consider someone who says: 'I had no choice, I had to do it — that's just who I am.' Sartre would say: no. You always have a choice. You may not like the alternatives. The cost of choosing differently may be enormous. But to pretend there was no choice at all is bad faith. It is a lie you tell yourself to escape the weight of your own freedom.