 The philosopher-mathematician G. W. F.  Leibniz[19]  (1646–1716) was greatly preoccupied with the problem of the composition of the continuum—the “labyrinth of the continuum”, as he called it. Indeed we have it on his own testimony that his philosophical system—monadism—grew from his struggle with the problem of just how, or whether, a continuum can be built from indivisible elements. Leibniz asked himself: if we grant that each real entity is either a simple unity or a multiplicity, and that a multiplicity is necessarily an aggregation of unities, then under what head should a geometric continuum such as a line be classified? Now a line is extended and Leibniz held that extension is a form of repetition, so, a line, being divisible into parts, cannot be a (true) unity. It is then a multiplicity, and accordingly an aggregation of unities. But of what sort of unities? Seemingly, the only candidates for geometric unities are points, but points are no more than extremities of the extended, and in any case, as Leibniz knew, solid arguments going back to Aristotle establish that no continuum can be constituted from points. It follows that a continuum is neither a unity nor an aggregation of unities. Leibniz concluded that continua are not real entities at all; as “wholes preceding their parts” they have instead a purely ideal character. In this way he freed the continuum from the requirement that, as something intelligible, it must itself be simple or a compound of simples.