Matter, Kant could readily agree with Leibniz, cannot be a thing in itself, stuff possessed of characteristics and qualities independent of human perception; what we call matter is an appearance (4:507). The true nature of mind-independent external reality cannot be described by reference to shape, contact or movement, which characterize only the objects presented to us (A265–6/B 321–2). He understood Leibniz’s reasoning in favour of monads as follows: It is impossible to conceive two material a