Kant's argument in his refutation of idealism has a lot of problems. I don't know what Fichte and Hegel said about the external world, when I looked for this before asking here they never appeared. I grant that strict solipsism begs the question in terms of assuming something which, by solipsism's own intuitions, couldn't be known (what's "out there", that according to solipsism would be nothing). But you could still be an epistemological idealist, committed to the idea that you can only know what you experience, and an ontological skeptic (in the sense of suspending judgment), not making any claim on wheter there is something or not besides your mind. The difference between the epistemological idealist relying on "what it feels" (his experience) and the realist's ("it feels like there's an external world") is that the latter could be easily interpreted as an instance of the former (the feeling of an external world would be just another experience), but it's difficult to grasp how one could legitimately make the same move starting from the external world ("the experience is caused at least in part by an external world"), since for postulating it you still have to differentiate the experience of the external world from it, and how could you "get out" of the experience to say something about the external world? My intuition is that, for pragmatic reasons, we rely on the inference of causality, which gives us the external world as the best explanation, but is there no better argument based on principles or something (I even suspect there is behind my pragmatic move, but I'm not seeing it)?