Realism in the Scholastic Period

Ibn Sina’s notion of the nature considered in itself had a tremendous influence on western medieval philosophers, once his works were translated into Latin in the latter half of the twelfth century. The notion of a neutral nature allowed Scholastic philosophers to avoid the commitment to a thing that is itself numerically one but simultaneously present in many individuals; yet, in the same stroke, it allowed them to locate some extra-mental basis for predication and classification.

The theories that thirteenth-century philosophers developed in response to the newly translated works of Aristotle and Ibn Sina are often referred to as versions of ‘‘moderate’’ realism. Moderate realism is routinely contrasted with ‘‘extremer’’ forms of realism. Medieval philosophers mostly knew of Plato’s ideas secondhand. As they understood him, Plato believed that universal forms could exist separately from all particulars and from all minds. Scholastic philosophers roundly rejected this form of Platonism.

There was one troubling feature of Ibn Sina’s notion of a nature in itself. Ibn Sina seemed to grant the nature in itself some measure of being (esse), yet he denied that the nature had any degree of unity. But it was a commonplace in Scholastic philosophy that something has being only in so far as it has unity. In other words, unity was considered to be a necessary concomitant of esse. Scholastic philosophers were, therefore, presented with a choice: either remove all esse from the nature as such, or grant that the nature as such has some measure of esse and, thus, some degree of unity (Owens 1957:4).

Thomas Aquinas chose the first of these options (De ente et essentia, ch. 3; cf. Owens 1957:5-7). The nature in itself had no being at all. It only had being in the mind, where it was truly universal, or in individuals, where it was a particular nature. Thus, if we were to take Adam and Eve and really strip away (not abstract with the mind) their matter, their accidents, their substantial forms, and their individual esse, we would find neither one nature nor two natures; we would find no nature at all. Nevertheless, in a very real sense, it is the same nature in numerically distinct individuals, and it is the same nature in the individual and in the mind. As one commentator puts it, numerically distinct individuals have the same nature because they are “numerically distinct realizations of the same information-content’’ (Klima 2008:§7). It is the same nature in the mind and in the individual because the mind is grasping the same information-content that is realized in the external world. To see what Aquinas is after, consider Klima’s analogy. There is no universal Moby Dick in addition to all the individual copies of Moby Dick. Nevertheless, it is true that all the copies of Moby Dick are the same book, because they share the same information. And if one were to memorize a copy of Moby Dick verbatim, it would be true that one’s physical copy and one’s mental copy are the same book.

John Duns Scotus chose the second option (see Ord. II, d. 3, pars 1, q. 1, [Spade 1994:57-68]; cf. Owens 1957:7-13). The nature in itself had some measure ofbeing, and hence, it had some degree of real unity. But it has less than numerical unity - that is, the unity characteristic of being an individual. The nature must have real unity, for if its unity were merely a product of the mind, then our natural inclination to group Adam and Eve together and call them both human would have no foundation in the order of things. The unity of the nature as such must be less than numerical, for ifthe nature were itselfnumerically one, then it would be this particular nature or that one. But if it were, say, Adam’s nature and Eve were also human, then Eve would in fact be Adam as well. Scotus knew that his brand of realism depends upon the intelligibility of a mode of unity that is real but less than numerical. Hence, he provided a series of arguments for the claim that there are real but less than numerical unities (op. cit., [Spade 1994:59-63]).