  Leibniz is not as clear as one would like him to be, for at this point in his career it is possible to read him as seeing that something is a substance so long as it has a soul or a substantial form, whereas later in his career it seems more clearly to be the case that the only substances are souls or soul-like entities, the monads. In other words, Leibniz can be interpreted as advocating, at least in this period, a kind of Aristotelian hylomorphism, in which substances are composites of matter and form. This has been the subject of debate in the field, but this entry cannot adjudicate the matter. (For more on this dispute, see Look 2010.)