In section I of Chapter 8 we observed that a certain constraint follows from the way in which the notion of a sum is defined, with regard to the types of correspondences allowed between individuals and their sums. Thus we found that if the xs and the ys have the same sum (at t),they must be coextensive (at t). This constraint provides us with a clue as to a way in which an account of wholes might be given according to which they are not construed as sums. To see this, however, we need to take a step back and examine the notion of a whole with a view to explaining, rather than simply taking for granted, its alleged connection with the notion of a sum.