Devil's advocate for why ontology is meaningless and vacuous.

[Mudhammam]

I would say no, there is no escape from solipsism. All we can do is make pragmatic assumptions. But we needn't even make all of them, really. For example, I don't have to assume anything is "real". It's real to me, and that's as good as it's ever going to get.

Yes, mathematics is an abstract system which is defined by strict rules. Such systems only need to be internally consistent. They may or may not relate to reality in any useful way. Mathematics is not scientific knowledge, though. It's a tool. It's used to describe scientific knowledge.

Is mathematics only a tool? For the most part, from what I have gathered, it has been thought of as a science, and one of the few in which any certain knowledge about reality can be had. The physical sciences, on the other hand, have more or less been thought to amount to but educated guesswork and opinion, given what you concede about the nature of consciousness and subjectivity.