Solipsism — From Latin solus (alone) joined to ipse (self), the term names 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 of other minds remaining undemonstrable. Three degrees of the doctrine are usually distinguished: metaphysical solipsism holds that only I exist; epistemological solipsism concedes that the world may exist but denies that I can prove it; and methodological solipsism simply takes one’s own mental states as the sole secure starting point for knowledge. Descartes’s hyperbolic doubt borders on this position by reducing all certainty to the cogito, though he overcomes it by appealing to God as guarantor of external reality. In analytic philosophy the issue returns as the “problem of other minds”: how do I know that other beings possess consciousness, when I have direct access only to my own? The argument from analogy, associated with John Stuart Mill, and inference to the best explanation are among the classical responses. Wittgenstein, in the Philosophical Investigations (from §243 onward), seeks to dissolve the problem through language: the celebrated “private language argument” shows that a language intelligible to a single speaker alone is impossible, since meaning presupposes public rules and hence a community. Husserl, in the Fifth Cartesian Meditation, confronts what he calls transcendental solipsism through a theory of intersubjectivity, in which the other ego is given by “appresentation” (Appräsentation). The central neighbouring concepts are thus the problem of other minds and intersubjectivity.
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