Part 3. Kant says that human ethical independence is so totalizing that not even the intrinsic grandeur and nobility of self-development can overcome moral duty. The human subjectivity must be accepted as capable of total moral accountability. This same subjectivity, just by chance, is also where Kant is going to stash all the phenomenal ooze, albeit in 12 discrete boxes. The universe is still mechanistic and objective, but your psychology is secretly holding it all together.
It's hard to explain what I think is so magical about this chain of transmission.
You start off with the dog-torturing asshole Descartes giving us some real drunk dad philosophy about how you can't trust anything. You start in this really grim position of this corpse-universe of efficient action grinding away empty matter on empty matter.
But by the end of this chain of critique, you actually come all the way around to this fascinating view of reality as intrinsically meaningful.
Part 4. Peirce says "no," these things attributed to the mind are all fake, the mind is fake, most of the phenomenal ooze is fake, EXCEPT there are a handful of transcendental bits that are actually totally real and necessary for signs to work. And signs working is the base reality now.
(Wait a minute, you may say: If the mind is fake then what is receiving all the signs? Of course the answer is that semiosis interprets itself, you silly goose. Semiosis is the atomic form of phenomenal ooze.)