The History of a Philosophical Misconception
by A. C. Grayling
(dialogue from a YouTube video)

“Well one thing that you can regard as progress in epistemology is that that great tradition beginning with Descartes and including Hume and coming all the way up to to Russell, himself, and A. J. Ayer, who was a teacher of mine at Oxford. They all shared the same starting point which was: from the private data of conscious experience. We have to try to build a bridge out to something which isn't ourselves -- to a world external to us. And... that was unsuccessful in Descartes' case. He had to help himself to a notion of a good God whose goodness is the guarantee that our experience tells us about a world because a good God wouldn't want to fool us about what our experience represents.

“But all his successors in the philosophical tradition thought that that was just too, you know, ad-hoc. So we'd have to find some other way. And Locke, and Berkeley, and Hume, and Mill, and Kant, of course, and all the way up to Russell and Ayer; they all tried (to answer) "How do you navigate a completely secure epistemological route from private conscious experience to an external world?" And they all failed.

And that is why in the 20th century you see in their very different ways Wittgenstein and John Dewey in the States and Heidegger, all of them saying, "No you don't start from the private data of consciousness. You have got to start in the public domain and work back inwards; instead of starting inwards and working outwards." And this is a whole different perspective on the idea of knowledge.

“John Dewey has this very interesting idea that the beginnings of our thought about how we have experience is in what he called the participant perspective. We have participated in a pre-existing reality which we wake up in; we find ourselves dealing with an outside world before we begin to reflect on the inner. And if we can try to make an argument out of that -- still quite hard to do -- but insofar as we've recognized that we need a change of perspective on this question that is progress.”