The composite nature of perceptions is examined further in terms of mereological structure. Manifolds of outer intuition are stretched out in a space that both differentiates between an object and its exact duplicate and underlies fine discriminations ad indefinitum of a single object’s manifold. However, there is also a unity of space that runs through all spaces contained in it. Since space is a form of perception, there is therefore also a unity that runs through all nested perceptual manifolds. For this to be possible, space has to be a special kind of whole, namely, what Kant calls a totum analyticum, i.e., a whole whose parts depend on it, rather than vice versa, i.e., not a totum syntheticum. It is argued that a particular mereological structure of space is a precondition for the organization of manifolds of perception. Another precondition is what Kant calls “affinity,” i.e., that perceived particulars – including tropes – can be represented in ways that are associable with each other. In neither case is the unity due to a combinatorial synthesis. In empirical cognition, such a synthesis can only trace out an order of a perceptual manifold that is already there.