People seriously undervalue the importance of "usefulness" in ontology. If I assume that the thing that others report is the same thing that I perceive, which g

People seriously undervalue the importance of "usefulness" in ontology. If I assume that the thing that others report is the same thing that I perceive, which given that they have a very similar slab of meat inside their skull as I do seems very plausible, then I can use my self-perception to learn about the interiority of 8 billion other people. I can even compare it to their reports to learn things about myself that would be hard to tell by observation! If I assume that my perception, for some reason, is only informative about myself, then I'm not even learning something about brains! I have to assume that I'm accessing an information stream that is only tangentially related to any sort of shared reality, and has certainly no bearing on other parts of it even if I assume it has bearing on "my" part of it for which, strictly speaking, I also don't have direct evidence. If there are two possible universes, one universe "A" where thought is valuable and useful, and one universe "B" where thought is solipsistic and extremely isolated, and also there is not just no evidence about which you are in but also philosophical arguments that there cannot ever be evidence about which you are in, I don't see why you should give universe "B" any serious thought. What are you standing to gain?