"Kant concludes §17 by contrasting the human understanding, which requires an act of synthesis to establish its unity, with another possible kind of understanding. This would be an understanding in which a manifold of intuition, and indeed the objects of that intuition, are given in its self-consciousness rather than being required for its self-consciousness. This would be an intuitive understanding, in contrast to the discursive understanding of humans, which only applies concepts to intuitions that are generated by sensibility. Kant says that we can frame no concept of such an understanding, or of an understanding whose material is intuitions not in space and time." (Critique of Pure Reason Lecture Notes: Transcendental Deduction G. J. Mattey)
I do not understand how there can be another kind of understanding apart from the first kind - "an act of synthesis to establish its unity". How can understanding be anything of understanding than the act of synthesis? I put in bold two phrases that I have been specifically trying to wrap my head around. The second one makes sense to me. We have self-consciousness only in relation to the world around us. How do we have self-consciousness by merely intuiting the world? That seems to be an absurdity!
Kant seems to contradict himself,
"In §18, Kant claims that, “Only the original unity of apperception is valid objectively” (B140). This means that the unity of apperception is a necessary condition for the presentation of an object." (Critique of Pure Reason Lecture Notes: Transcendental Deduction G. J. Mattey)
If I understand correctly that "unity of apperception" is only an active working of the understanding that brings the object to cognition to the perceiving subject.