Solipsism is the philosophical position that only one’s own mind is certain to exist. Its core claims:

• Epistemological solipsism: I can know only the contents of my own consciousness; knowledge of external minds or an external world is not just uncertain but unjustified.
• Metaphysical solipsism: Only the self (or the self’s mental states) truly exists; other people and the external world are mere appearances or constructs of the self.
• Methodological (or methodological scepticism) variants treat solipsism as a skeptical challenge prompting careful justification of claims about others and the external world, not necessarily a committed ontological stance.

Key implications and objections:

• Raises problems for intersubjectivity, ethics, and communication (how to justify other minds, moral obligations).
• Common objections: it is self-defeating in practice (language and social life presuppose others), and it’s unfalsifiable and hence epistemically weak.
• Philosophical responses include inference to best explanation (positing other minds is simpler) and appeals to shared behavior and continuity of experience.

References: Descartes’ methodological doubt, Berkeley’s idealism (related but not solipsistic), and later discussions by G.E. Moore and Wittgenstein on other minds.