The Kantian project as I understand it was an attempt to overcome the sceptical problem as to how knowledge is possible given that the external world could be radically different from the way in which it is represented as being at the internal or phenomenal level. Kant’s Copernican revolution was to propose that knowledge could only be achieved, and only needed to be achieved, of the necessary conditions for internal consciousness and that attempts to achieve knowledge of the world as it is in-itself are misconceived. My (probably un-original) reasons for thinking that Kant’s project fails are set out fairly informally as follows:
1. Kant’s epistemological standards are such that we cannot have knowledge that P if it is epistemically possible that not P.
2. An adequate theory of representation allows that a merely represented object may be ontologically indistinguishable from a real or veridical represented object, otherwise a represented object characterised by the wrong properties is represented.
3. Such an adequate theory of representation allows that the phenomenal mind may be the merely represented object of a much less sophisticated representation, i.e. the introspecting Kantian has no way of knowing whether or not they really exist. (Not controversial for a Kantian happy to work at the level of appearances.)
4. There are or can be representations of impossibilia.
5. Not knowing whether or not whether of not they really exist, the Kantian has no way of knowing whether they are an impossibilium.
6. If it is epistemically possible that the structure of the Kantian’s phenomenal mind is impossible then it cannot be known that the structure of the Kantian’s phenomenal mind is possible.
7. If it cannot be known that the structure of the Kantian’s phenomenal mind is possible then it cannot be known that said structure is a necessary condition of consciousness, seeing as knowledge of necessity assumes knowledge of possibility.
8. Thus, the Kantian has no knowledge by her own standards.
This suggests what is obvious these days: our epistemological standards cannot require that is not possible for us to be wrong in order for us to have knowledge. Now, all we need is an adequate definition of knowledge, and that brings me up to the middle of the last century in epistemology.
In quantum physics knowledge is now defined as placing an object at a particular place or time in a coordinate system.
Perhaps Kant was suggesting the same for phenomenal knowledge?
I don’t think that physicists get to define what knowledge is.
For example, how do you account for one’s knowledge that knowledge is the placement of an object at a particular place or time in a coordinate system by the placement of an object at a particular place or time in a coordinate system?