In my more naive days, I thought two things (well, I thought more than two things, but for present purposes, only two are of importance): that causality was empirical and that Kant was way overrated. I know realize that causality is a metaphysical, not empirical category, but I still think Kant is way overrated. What Kant has showed me, however (and, if I may say so, through no small effort of my own – Kant isn’t exactly a paragon of clear writing) is that the human mind is not simply a passive receiver of empirical data from the world outside my mind.
While I do agree with Russell that the mind has at times been given a place of prominence in philosophy and metaphysics that it doesn’t necessarily deserve, there can be no real doubt that in at least this one instance, Kant’s idea that the mind plays an active role in some kind of creation of the world of our experience. If the self was, for example as Hume thought, a bundle of impressions (granting for the sake of argument that this wasn’t an incoherent notion informed by radical empiricism), then there couldn’t really be any experience of the world because there would be no principle by which experience of sense-data could be organized to form any kind of coherent unity of experience at all. There would be only sense-impressions, one after the other, and knowledge of particulars only isn’t any kind of knowledge at all.