In the Resolution of the Second Antinomy of the first Critique and the Dynamics chapter of the Metaphysical Foundations of Natural Sciences, Kant presents his critical views on mereology, the study of parts and wholes. He endorses an unusual position: Matter is said to be infinitely divisible without being infinitely divided. It would be mistaken to think that matter consists of infinitely many parts-rather, parts "exist only in the representation of them, hence in the dividing". This view, according to which parts are created through division somehow, was criticized as obscure early on, and has not received much attention since. Against this trend, I show how a coherent position, which I call Mereological Conceptualism, can be extracted from the sparse textual basis. There was a time when the dispute respecting monads employed such general attention, and was conducted with so much warmth, that it forced its way into company of every description, that of the guard-room not excepted. There was scarcely a lady at court who did not take a decided part in favour of monads or against them. In a word, all conversation was engrossed by monads-no other subject could find admission. [...] As this controversy has made a great deal of noise, you will not be displeased, undoubtedly, if I dwell a little upon it.