 Kant characterizes synthesis as “the act of putting different representations together, and grasping what is manifold in them in one cognition” (A77/B103); it is a process that “gathers the elements for cognition, and unites them to form a certain content” (A78/B103). Synthesis takes multiple representations – in Kant’s terminology, a ‘manifold’ – and connects them with one another to produce a single further representation with cognitive content (Patricia Kitcher 1990, 2011). This process employs concepts as modes or ways of ordering representations. A claim critical to the Transcendental Deduction is that it is the categories by means of which manifolds of our representations are synthesized. Since the understanding of the subject is the source of the categories, and also a faculty that yields synthesis, the subject plays a crucial role in mental processing. It is important for Kant’s view on mental processing that this subject is distinct from its representations, and this is another respect in which it differs from Hume’s theory.