What is a solitarist?

Answer 1

Solipsism is the philosophical position that one is a solitary being, and everything perceived as external to oneself is actually a figment of that solitary brain.

Basically, since we can't conclusively prove that the things we sense are separate from ourselves and also real, then one might conclude that they are a 'brain in a jar' or the like.

btw: I'm assuming you meant solipsism.