 It is only the third principle, (P.4), that appears to provide a full formulation of the idea that a whole cannot be decomposed into a single proper part. According to this principle, every proper part must be “supplemented” by another, disjoint part, and it is this last qualification that captures the notion of a remainder. Should (P.4), then, be incorporated into M as a further fundamental principle on the meaning of ‘part’? 