And why is it such a problem?
One of the most serious and extensive controversies of the Latin Age of philosophy was that of universals. The Greek philosophy of antiquity, and its transmission into the Latin Age by Boethius and through the Islamic tradition, had long discussed the question of whether the way in which we know things–universally (as, I don’t just have cognition of this or that human, but know humanity)–has a direct and immediate correspondent in the objects we encounter in the world–particulars–and how that relation worked. While the Greek and Islamic philosophers influencing the Latins generally held for some identity of thought and thing, some of the Latins demurred: the so-called nominalists, who held that the supposed universals are mere “names” (in Latin, nomina, hence, nominalists). The most notable, well-known of the nominalists, living in the the later years of the “High Middle Ages”, was William of Ockham (c.1287-1349).
But nominalism–the rejection that there exists a cognition-independent reality to universals–had a first “florescence” some 250 years prior to Ockham, evidently instigated by Jean Roscelin (c.1050-1120). Roscelin was challenged, but poorly, by William of Champeaux (c.1070-1130); both were countered by a common student of theirs, Peter Abelard (c.1079-1142 – of “Abelard and Heloise” fame; cf. Maurer 1962: Medieval Philosophy: An Introduction, 61-65). Abelard’s own view was far more subtle than the views of his teachers–Roscelin holding that a universal word is a flatus vocis (which you might legitimately translate as “verbal fart”) signifying no object, and Champeaux holding that individuals are possessed by the whole of their universals; and yet because the relative paucity of Abelard’s extant writings, as well as their nature (generally, commentaries or glosses on the works of others), precisely characterizing his view remains a challenge.
It has often been suggested, and not without good reason, that Abelard’s view is comparable to that of John of Salisbury (1115-1180), termed “conceptualism” (Deely 2010: Medieval Philosophy Redefined, 132) wherein: “the mind recognizes the same or similar characteristics in different individual objects and conveniently gathers these differences into one mental concept or idea, which provides the meaning for the universal or general term, the spoken sound or written character string with which the concept is then associated.” While this may not be as harsh as the flatus vocis of Roscelin, it hardly resolves the challenge which nominalism poses; that is, (Deely 2010: 133): “The claim of nominalism is that there is no direct referent, no proper significate, for general terms on the side of the object as thing. This claim is hardly met by pointing out that such terms depend in their meaning on a subjective ground in the mind.”
This latter position–the conceptualism of John of Salisbury–is much the same position of much modern philosophy. That is, while empiricism (which has more or less “won out” over rationalism among the descendants of the moderns) recognizes the reality of adventitious sense experience, it does not recognize the reality of generality independent of the mind.
Though nominalism subsided in the middle period of the “High Middle Ages”, in which a more moderate realism under the influence of Aristotle came to bear, it was revived in the work of William of Ockham, who presented a sophisticated theory which deftly obscured quite an impressive bit of nonsense. That is, Ockham held there to be nothing other than individuals (cf. Maurer 1962: 277-81). At the heart of his objection to the notion of universals is seeing a way in which they might possess existence; for Ockham conceived existence on the model of substantial being alone, in esse, i.e., being as in a substance–either in se (in itself, as a relatively-indepedent substance, such as a human) or in alio (in another, in a substance as an accident, such as the color of a human’s hair). Anything universal in itself, or general, could not be either a substance or an accident; for then it would be subsisting within an individual and therefore constrained to particularity–not predicable of others, not universal, not general.
The nonsense here, of course, is that if a sign is an individual thing–a sign being for Ockham the means whereby “universality” occurs, namely in that one individual thing, the sign, can signify many (cf. Maurer 1962: 280-81)–there is no explanation for the existential status of its connection to those things its signifies; that is, if a sign is not a relation, or does not entail a relation, how can it bring about a connection between the the mind and its object? (Cf. Deely 2010: 326-27).
This allows us to give a definition for nominalism, which comprises all its forms: the denial that relations as such possess an ontological status independently of the mind, or, being effectively the same thing, if they do exist they cannot be known.
In stark contrast to the nomainlists, some other Latins, including Thomas Aquinas, discuss relation as something which is not merely a descriptor that we add to substances, but as something–a mode of being–in its own right. Thus, the relative was divided into the relativa secundum dici and the relativa secundum esse. These two terms are translated–both into alternative Latin formulations and English–in many and many bad ways. Without prolonging the issue: the relativa secundum dici designates the fact that, in most situations, we cannot talk about substances or their accidents without talking about them as related to other things–as mover and moved, to the right of, behind, the cover (of), the head (of), etc., etc. In contrast, the relativa secundum esse signifies the relation itself, as an existence distinct from albeit dependent upon the things related (cf. Thomas Aquinas 1266-68: Summa theologiae prima pars, q.13, a.7, ad.1 — but be wary of the translation; relativa secundum esse is poorly rendered as “predicamental relation” and relativa secundum dici as “transcendental relation”).
While Aquinas does not discuss the twofold sense of relation at any great length, the belief in the existence of relations themselves as irreducible to the things related has tremendous importance for one’s theory of knowledge: for it not only allows the knower a real connection to the known by something not individual, it makes for an intelligible fabric of all other things. The question of universals seldom turned around an extreme realism–that is, that the universal itself is a real being, such that there exists a humanity, either as an thing bisecting all the individuals, or as a thing separate from the individuals as an extrinsic form in which they participate (as members in a church might make up a “congregation”)–but much more circled around the question of whether some form in the individuals was really the same among them all or whether they were merely incidentally similar to one another, grouped under a common heading insofar as we make that comparison through our own minds. Holding that relation exists not only through the activity of our own minds but in the world independently of our cognition helps to resolve the issue–for we can discern the sameness of form between a plurality of individuals not merely by the correspondence of accidental, visible properties, but by the common characterizing acts which distinguish one kind from another, by their ordination to some end.
Without such a belief, on the contrary, everything falls apart.
I mean not just our knowledge of things but also our moral justifications. It is little surprise that in the thoroughly nominalistic worldview, social contracts are often proposed as the means for establishing moral norms (while “ethics” becomes subjectivized as one’s “personal code”). These primarily end up circling around “negative duties”, such as to not intentionally cause harm, not deceive, and so on. Conversely, the good of life is turned into the pursuit of value (a relation between the one valuing and the thing valued–and therefore not something which exists independently of the mind), which is permitted so long as it does not infringe upon the negative duties of the social contract.
The social contract, being by stipulation (thus cognition-dependent; and specifically by a stipulation held as separate from anything cognition-independent), can be changed: either explicitly, by the direct intervention of whatever forces responsible for governance, or implicitly, as the populace interprets the meanings of the words of the contract in a shifting intellectual landscape.
Or, in other words: if nominalism is true, everything is permitted.