 The first principle, (P.4a), is a literal rendering of the idea in question: every proper part must be accompanied by another. However, there is an obvious sense in which (P.4a) only captures the letter of the idea, not the spirit: it rules out the unintended model mentioned above (see Figure 2, left) but not, for example, an implausible model with an infinitely descending chain in which the additional proper parts do not leave any remainder at all (Figure 2, center). 