 It’s widely agreed that a crucial feature of the second step is the claim that our intuitions of space and time are constituted in such a way as to necessitate the unification of the manifold of appearance by the application of the categories. In the Transcendental Aesthetic, Kant aimed to show that space and time are forms of our sensible intuition, and that for us appearances can only occur in accord with these forms. But now, in the note to B160–1, Kant draws our attention to the fact that space and time are not only forms of intuition, but are intuitions themselves, and that they are intuitions that feature unity. What’s more, Kant specifies that this unity ‘precedes all concepts, though to be sure it presupposes a synthesis, which does not belong to the senses but through which all concepts of space and time first become possible.’ By the synthesis that is presupposed ‘the understanding determines the sensibility.’ So the unity of space and time is to be explained with reference to the effect of the understanding upon sensibility itself (Longuenesse 1998: 211–33; Keller 1998: 88–94; Dickerson 2004: 196–201; Pollok 2008; Vinci 2014: 197–229; Onof and Schulting 2015; Allison 2015: 374–432; Rosefeldt 2022).