Solipsism — From Latin solus (alone) + ipse (self). The extreme epistemological position that only one’s own mind and its states can be known with certainty; the existence of the external world and other minds is undemonstrable. Three forms are distinguished: (1) metaphysical solipsism — only I exist; (2) epistemological solipsism — the world may exist, but I cannot prove it; (3) methodological solipsism — I take only my own mental states as a secure starting point. Descartes’s hyperbolic doubt borders on solipsism by reducing all certainty to the cogito, though he overcomes it by appealing to God as guarantor of external reality. The “problem of other minds” in analytic philosophy extends the question: how do I know that other beings possess consciousness? The argument from analogy (Mill) and inference to the best explanation are classical responses. Wittgenstein (Philosophical Investigations, §243–315) dissolves the problem through language: the “private language argument” shows that a purely private language is impossible — meaning presupposes public rules, hence community. Husserl confronts transcendental solipsism through the theory of intersubjectivity (Fifth Cartesian Meditation), resorting to the “appresentation” (Appräsentation) of the alter ego.
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