Maritain rejected the emphasis on epistemology characteristic of modernity (and then postmodernity) and, seeing himself as an heir of the pre-modern philosophy of Aquinas, argues for the priority of ontology over epistemology(Sweet, 2008). Rather than simply restating the thought of Aquinas, he instead saw his task of revising it(Sweet, 2008). There are times at which he simply agrees with Aquinas, for example, against Duns Scotus, in his adoption of analogical concepts against Scotian univocity(Sweet, 2008). He also agrees with Aquinas that the apparent problem of unity and plurality (how something can be a distinct individual yet still be a member of a class) as well:
Maritain follows Aquinas: that we have to distinguish what a thing is (its nature or essence, which it shares with things of the same kind), from the fact that it is (i.e., that it has its own 'act of existing'). When it comes to the analysis of the nature and the unity of sensible beings, including human beings, Maritain employs Aquinas's distinction between the form and the matter of a thing; nature or essence reflects the form, whereas the individuality is determined by the matter(Sweet 2008)
Sweet, William, "Jacques Maritain", The Stanford Encyclopedia of Philosophy (Fall 2008 Edition), Edward N. Zalta (ed.), URL = <http://plato.stanford.edu/archives/fall2008/entries/maritain/>.