Solipsism, of course, is the belief that only you exist; that what you experience as the universe is an illusion created by your mind, with no external input of any kind, because there is nothing external to you. In most ways solipsism is a useless idea, inasmuch as it can’t be proven to be true, and once accepted, it really doesn’t lead to anything else, in terms of philosophy, insight into life, or development of one’s self. This is pure or strong solipsism, but there is a spectrum of lesser solipsisms, which hold in varying degrees that the universe is a construction of the mind, constrained by socially-based consensus, and, in its mildest forms, by some kind of external reality. It is possible to derive a kind of cultural relativism from these milder forms, by which one would not judge any world view as being more or less valid than any other.
I certainly hold that each of us constructs their world in their minds, and that we behold our constructions rather than directly experiencing external, presumably physical reality. Lest I spawn a homunculus, I think its better to say there actually is no beholding of the construction, but rather that the constructing is the beholding and the constructor is the beholder. I also hold that one’s construction is constrained by external physical reality as well as by the consensual reality of one’s social group. But I am a little uncomfortable knowing that strong solipsism might actually be the case.
But I recently had an insight that, for me at least, forever eliminates any possibility of strong solipsism. The insight is that dreaming is very different from waking experience. This is because dreaming is subject to no constraints, either from external reality or from social consensus. Dreaming is free to be inconsistent, non-causal, nonsensical, magical, and crazy. If strong solipsism were the case, then waking experience, also free of external constraints, would be equally inconsistent, non-causal, nonsensical, magical, and crazy. I leave out the waking experience of people in psychedelic, mystical or psychotic states of consciousness, where visions or hallucinations are so strong that they constitute a world independent of external physical reality. But my waking experience is nearly always consistent, continuous, generally regular, often predictable, and really quite different from my dream experience. There must be external constraints, either consensual constraints deriving from one or more beings outside myself, or from these beings as well as from external physical reality. The physical reality, if one accepts that it exists, is unknowable, but its constraints are inferable and its apparent regularities describable. At this point, I don’t know how to determine if the world is a collective hallucination of myself and other beings, or if there is an external physical reality, but at least I know I am not alone.
I dream, therefore others exist.