QUALITIES, REAL. Also called real accidents, these constitute a special category in scholastic philosophy distinct from the traditional Aristotelian categories of substance and mode. Introduced by the scholastic Francisco Suárez, this category includes beings that are distinct from substances insofar as they do not naturally subsist by themselves, but that are distinct from modes insofar as they can miraculously subsist by themselves (this is also why such qualities are called “real”). Descartes protested that the very notion of a non-substantial being that can subsist on its own is incoherent, since anything that can so subsist counts as a substance. He further concluded that, in the case of body, all that can be said to exist is quantified substance and its modes.
This conclusion in Descartes was controversial in the early modem period primarily because it was seen to conflict with the Tridentine doctrine that in the Eucharist the “species” of the bread and wine remain after transubstantiation. Following Suárez, scholastics identified these species with real qualities that miraculously subsist apart from the substance of the elements. In his Fourth Set of Objections to the Meditations, Antoine Arnauld emphasized that this scholastic position provides the main basis for theological opposition to Descartes’s system. In response, Descartes protested that official Church declarations do not require the belief in real accidents, and that the persistence of the species can be accounted for in terms of the persistence of the surfaces or boundaries that contain bodies. He noted that this understanding of species is allowed by his system since the surfaces are only modes. In the original version of his response to Arnauld, Descartes added the charge that the scholastic appeal to real qualities is contrary to Church doctrine since it suggests that there is in fact something substantial in the elements that remains after consecration. Descartes’s editor Marin Mersenne excised this charge from the 1641 Paris edition of the Meditations out of fear that it would compromise the attempt to win the approval of the Sorbonne. However, Descartes reinserted the excised portion into the 1642 edition of this text, published in Amsterdam.
QUANTITY. The classical understanding of quantity defined it as anything capable of greater or less. Thus, lengths, angles, and times are all quantities because they can be increased or diminished. There is a further fundamental distinction between continuous quantities (known as magnitudes) and discrete quantities (or multitudes). The former are the infinitely divisible objects of geometry while the latter are studied in arithmetic. Descartes held that quantity could only be conceptually distinct from a thing having that quantity, so that there are no self-subsistent abstract quantities over and above a number of measured quantity. As he put the matter in the second part of the Principles. “There is no real distinction between quantity and extended substance, but only a distinction in our thought, like that between number and the thing which is numbered” (AT, vol. VIIIA, p. 44).