Lately I’ve been hearing a lot of talk about (philosophical) idealism. I qualify it as philosophical to distinguish it from casual meaning of optimistic. In philosophy, idealism is a metaphysical view about the nature of reality — one that I’ve always seen as in contrast to realism.
What caught my eye in all the talk was that I couldn’t always tell if people were speaking of epistemological or ontological idealism. I agree, of course, with the former — one way or another, it’s the common understanding — but I’m not a fan of the various flavors of ontological idealism.
It seems downright Ptolemaic to me.
In debates (or even just discussions) people sometimes ask how we know the physical world is really there. A variation asks how we know that what we perceive as the real world is the same as what other people perceive. (One example of this is the inverted spectrum.)
The most accurate answer is: We don’t. Not for sure, anyway. There is at least one assumption built in, but it’s one we have to make to escape our own minds. According to ancient philosophical tradition, the only fact we know for sure is that we ourselves exist. (Although I think there’s an argument to be made about a priori knowledge.)
But, as with the excluded middle, accepting reality as an axiom seems almost necessary if we’re to move forward in any useful way.