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 
Logos con carne 