solipsism the doctrine that there exists a firstperson perspective possessing privileged and irreducible characteristics, in virtue of which we stand in various kinds of isolation from any other persons or external things that may exist. This doctrine is associated with but distinct from egocentricism. On one variant of solipsism (Thomas Nagel’s) we are isolated from other sentient beings because we can never adequately understand their experience (empathic solipsism). Another variant depends on the thesis that the meanings or referents of all words are mental entities uniquely accessible only to the language user (semantic solipsism). A restricted variant, due to Wittgenstein, asserts that first-person ascriptions of psychological states have a meaning fundamentally different from that of second- or thirdperson ascriptions (psychological solipsism). In extreme forms semantic solipsism can lead to the view that the only things that can be meaningfully said to exist are ourselves or our mental states (ontological solipsism). Skepticism about the existence of the world external to our minds is sometimes considered a form of epistemological solipsism, since it asserts that we stand in epistemological isolation from that world, partly as a result of the epistemic priority possessed by firstperson access to mental states. In addition to these substantive versions of solipsism, several variants go under the rubric methodological solipsism. The idea is that when we seek to explain why sentient beings behave in certain ways by looking to what they believe, desire, hope, and fear, we should identify these psychological states only with events that occur inside the mind or brain, not with external events, since the former alone are the proximate and sufficient causal explanations of bodily behavior. See also DESCARTES , EGOCENTRIC PRE — DICAMENT , PHILOSOPHY OF MIND , PRIVATE LANGUAGE ARGUMENT , SKEPTICIS. T.V.