• Kant begins §§27-35 by saying we can now remove “Hume’s doubt.” His way of removing it is to say it is quite legitimate regarding things in themselves but not regarding our experience. This discussion can be divided very roughly into two parts. Sections 27-30 tend to focus on Kant’s view of the function of the pure concepts of the understanding (i.e., causality and the like) while §§31-35 focus on the error of attempts to apply these concepts to things in themselves. Along the way, Kant introduces the convenient term ‘noumena’ for things in the themselves. (‘Noumena’ is the plural form; ‘noumenon’ is the corresponding, but rarely-used, singular form.)

• Although §§36-38 reiterate Kant’s idealism, they also have a good deal to say about the relation between pure intuition and the pure concepts of the understanding, so they tell us something about how he thinks his accounts of pure mathematics and pure natural science fit together.

• Kant’s “appendix” to part II (§39), speaks of the systematic character of the tables in §21. The systematic character of Kant’s various tables tends to seem less obvious and less important to others than it did to him. However, his discussion of it here is important for an incidental reason: he introduces the term ‘categories’ for the pure concepts of the understanding. Although this is his first use of the term in the Prolegomena, he used it throughout his discussion of these concepts in his first Critique, so it is the way most people refer to them, and he will use the term frequently in the rest of the Prolegomena.