solipsismus

Solipsismus comes from Latin solus (alone) and ipse (self) — alone-self, the self by itself. The term was coined in the eighteenth century to name a position as old as philosophy itself. If all you can directly access is your own experience, how do you know anything else is real? Descartes' cogito ergo sum in 1637 reached the same edge: the one thing you cannot doubt is that you are thinking. Everything else — other minds, the physical world, your own body — could be an illusion.

George Berkeley pushed the problem further in the early 1700s. His idealism held that material objects exist only as perceptions in minds. Samuel Johnson famously kicked a stone and declared 'I refute it thus,' but Johnson's refutation was itself a perception. The logical circle could not be broken from the inside. Gottfried Wilhelm Leibniz used the word solipsismus in correspondence to describe the position he found both irrefutable and absurd.

The problem is not that solipsism is persuasive. The problem is that it cannot be disproven. Every piece of evidence you bring against it — other people's behavior, scientific instruments, the consistency of physical laws — is itself something happening inside your experience. The argument eats its own tail. Philosophers have generally responded not by refuting solipsism but by showing that it is unlivable. Wittgenstein argued that a private language is impossible, which undercuts the solipsist's starting point.

The word entered casual use in the twentieth century to mean extreme self-centeredness — narcissism with a philosophical alibi. This usage misses the original point. Solipsism is not selfishness. It is a logical trap. The solipsist does not believe other people do not matter. The solipsist cannot prove other people exist.