I have just finished listening to the tapes of Bernstein on Kant’s Critique of Pure reason. (See www.bernsteintapes.com). So I feel like I am in a better position to answer this question now than I might have been earlier when I thought I knew something about Kant but had read it so long ago that it was hazy in my memory.
What Bernstein says is that for Kant Ontology is basically Epistemology. In other words the essence of the Copernican turn of Kant was to transform ontological questions into epidemiological ones about the necessary conditions for the possibility of experience. That makes all ontological experiences filtered though the lens of the Transcendental Subject, i.e. the one who produces the Apriori Syntheses that the empirical ego experiences, and that the Analytical philosophers analyze after the fact. Bernstein does a regressive reading of Kant, i.e. does not over inflate the claims about what Kant is trying to achieve. So he is giving us a minimalist Kantian interpretation, so that gives us a criteria by which to judge the progressive readings, i.e. the readings that see Kant as claiming too much compared to what he can deliver.
What is strange is that there are almost as many commentaries on Kant as there are on Plato, yet the Kantian commentaries are extremely weird for the most part because they all try to put their own philosophies in the mouth of Kant, my favorite example is that of Heidegger, which Bernstein dismisses but which I still find enlightening. But I searched and searched for a commentary on Kant that I could understand and which did the minimal permissible projection onto Kant of strange ideas. And the only one that I found that fit this bill back in the 1970s was that of Patton. Bernstein mentions Patton in a positive light, but points to other more recent commentaries that he likes, which I hope to read someday. Bernstein says that Kant is Transcendental Idealist who believes that you can only be a Transcendental Realist through Transcendental Idealism. And of course this is because we only experience the world via our consciousness and so what ever the world might be out there, we cannot escape our filtering it by our consciousness and need to take that into account. Basically this means that there are Apriori syntheses produced by our unconscious that appear to us in consciousness as if effortlessly generated, and so we do not notice the fact that these experiences are generated by our complex biological structures because they appear as given immediately and spontaneously. In a way we can see Kant’s breakthrough as the first glimmers of our understanding of the role of the unconscious as the part of the iceberg below the surface of consciousness which is merely a very thin veneer on the top of some very complex and incomprehensible processing of information that gives us our world and allows us to act seemingly effortlessly within it, for the most part. There were many subtleties of the arguments of Kant that I did not appreciate prior to listening to Bernstein’s lectures.But one thing that I can say to answer the question at hand is that ontology is completely mixed up with if not identical to epistemology in Kant. His stance is much closer to Husserlian Phenomenology than I imagined, and I thought that they were almost identical to begin with. Kant still has a dogmatic streak in him, and so he states his critique of dogma dogmatically. Husserl instead says this is a territory to be explored and opens it up to exploration and interpretation, and thus carries on the spirit of the critique further than Kant was able to do, as he was still dogmatic in his break with dogma in philosophy, i.e. positing final statements about the status of objects of experience rather than delving deeper into the phenomenology of those experiences themselves. I really listened to Bernstein in order to reset my understanding of Kant so I could connect it to the deflationary reading of Hegel that he presents in his other lectures. Kant represents a point of sophistication in philosophy that we may never achieve again. All philosophy after Kant is moving in his orbit. He thought he could show that Epistemology IS Ontology. And his arguments are pretty deep even if ultimately they fail even in the regressive reading of Bernstein.
Husserl attempted to solve some of these problems by looking in a more detailed way into the structures and processes of consciousness itself. But ultimately he came up against the same wall, i.e. the noumena, i.e. bracketing. Bernstein says for Kant appearances were the reality, but he still reserved the noumena which he believed had no remainder. But most interpreters believe that there is a remainder, that is there even though we cannot know it. What I did not realize that Bernstein emphasizes is that that Kant only brought up the term in order to define it so he could say there was no remainder. Bracketing takes that remainder what ever it is that we can never know out of play. But that same bracketing produces solipsism and the problem of intersubjectivity (i.e. the social). But according to Walton, Husserl in his later work discovered the idea of replacing bracketing with the horizon of the world, which Heidegger used with great effect in Being and Time stealing some of Husserl’s thunder. Bernstein said that Heidegger basically misunderstood Kant’s philosophy of time. But the philosophy of time that Heidegger took from Husserl is that of Internal Time Consciousness which was the one book that Heidegger edited of Husserl’s. In fact Bernstein’s final critique of Kant is that he thought Kant applied too monolithic a notion of time to phenomena. And Husserl’s internal time consciousness diagram is precisely an expansion of our notion of time beyond “Objective Time”. Kant’s argument about time hinges on the difference between serial and parallel time. Objective time for Kant is simultaneity of the systematization of objects. This difference revolves around the distinction between Freedom and Causality, and that revolves around the reversibility or irreversibility of our own action (house verses river boat analogies). Husserl instead uses a sedimentation analogy that hearkens back to the Orlog (cf Well and Tree by Bauschatz) of Indo-European fame. It is a model in which time has depth and so there is an extra dimension to resolve the problem that exists in the schematization of objects in time that Kant’s argument in the analogies runs into and which Bernstein criticizes. It is a better answer than the one that Bernstein answers which is evolutionary time, because Internal time Consciousness is a subjective time, rather than an objective time that encompasses the species. So this suggests that Heidegger was not far wrong by emphasizing the analysis of time in Being and Time, and seeing the equiprimodiality of the moments of time as the place to start, but instead of emphasizing memory as Husserl had done, Heidegger emphasizes the future instead.
At any rate I recommend listening to Bernstein’s lectures on tape for a more complete answer to this question, and a far more authoritative one than I can give.