You’re referring to the impossibility of viewing the noumenal world, yes?
No, not exactly. In Kant’s thinking the phenomenon we perceive at least indicates that there is a thing truly underlying this phenomenon, the thing-in-itself or noumenon. If you like to say so, there is no phenomenon that does not stem from an objective object; or, to express this idea more crudely, there are as many noumea as there are phenomena. - But what the critique I had in mind displayed was that Kant’s refutation of idealism only carries to the point of establishing an undifferentiated, totally homogenous mass of noumenal matter, if I may say so. The phenomena, that is, their content, may be wholly unrelated to this mass of objectivity. Hence we cannot be sure if there is any specific objective object that is linked to the image of a house, a rabbit or a human we perceive. There may even be no thing-in-itself behind the thing(apart, of course, from the faceless, curveless, flattened mass of noumenal matter, which properly is no thing at all). -
It’s a little like the question whether there truly are rabbits, houses and humans or whether it’s not just all an all-encompassing cloud of energy to which only pertains the quality of reality, all the rest being illusions.
To lend a keener sense of contrast to the two different concepts, I’ve talked about the ‘noumenal mass’. Of course this must not be so. The noumenal world may be highly heterogenous. But in Kant’s idea there is a relation between a thing and a thing-in-itself. That’s ultimately the reason why it’s called the thing-in-itself of the thing. - The critique, however, laid open that Kant never proved such a relation to exist.
However this may be, I found the essay again I draw from now and copy here the decisive statement:
Kant’s argument, in fact, seems to have missed a step. Kant, I think, has merely shown that the idea of time-consciousness requires some objects “outside me.” That, however, is some way away from our having an immediate experiential grasp of them. What Kant is doing thereby is conflating the conditions of inner experience—namely, that there are objects outside us—with inner experience itself which is nothing more than consciousness of my existence in time. There is an interesting view of experience contained here. The certainty of the existence of external objects does not derive from their being experienced as actual (with all their properties and determinations): rather they are certain insofar as they provide the conditions of inner experience. I think therefore that Kant is drawing the wrong conclusion from his argument. This is because of a missing step. He shows that we require external objects, but he does not show that there need be any correspondence between these objects and our representations of them.13 His argument does not demonstrate the objective reality of the content of our representations, merely the consciousness of their order. And this leaves the skeptic with room to maneuver.
ucd.ie/philosophy/staff/oconnor/kantsref.pdf
As yet, I haven’t read any better defense of the reality of an external world than Kant’s. But I want to make sure I’m not misunderstood here. There are many scathing critiques of Kant’s argument extant. Also I haven’t even remotely spend the time and the effort on this question it truly deserves. This is, in part, due to the fact that I’m a basic believer - I believe in the external world, in other subjective minds, in objective moral values, in God; in other words, in everything one associates with the dictates of common sense(I have a feeling you’d rather prefer to exclude God from this list but this is of no issue here - I’m just relating my private perception of things). - Well, but if only for the sake of argument we take for granted that Kant has done a masterful job and inaugurated himself as the king of logic in his defense of an external world, if we assume now that it would bespeak an immaturity of mind and a lack in the capability of logical reasoning if one failed to agree with him, still, still the fact remains that Kant only could prove, by the natural consequences of his very own principles and lines of argumentation, the undifferentiated external world, as is shown in the essay linked to above.
