Realism vs Nominalism

I've been interested in epistemological questions, and the question of Realism (the notion that logical notions possess a kind of "physical existence") versus Nominalism (that logical notions do not exist physically) gets down to several fundamental questions in both epistemology and ontology.

There is a divide in philosophical discourse which has continued to persist for thousands of years. The ideological divide concerns a fundamental question about how the universe is rationally perceived: do immaterial objects of rational thought truly exist independently of the mind? How one answers this question determines whether one is a metaphysical realist or a nominalist; a realist would answer the question in the affirmative, and the nominalist in the negative. The fundamental ideas behind this difference in ontological reasoning are largely present in the ancient clash between Plato's and Aristotle's views of how knowledge of the universe is obtained. Both philosophers formulate their theories in terms of physical entities and their respective properties; everything must be explained in terms of these two things. Plato emphasizes the preeminence of properties, whereas Aristotle extols the concreteness of physical entities. Thus, one of the catalysts that leads to debate on the ontological status of immaterial entities is an examination of Aristotle's work on categories. The question arises: are genera and species real, or do they consist solely in human imagination?

Part of what makes this question of existence so important is the inevitable entanglement between epistemology and ontology. In the end, one can only have a justified true belief about that which truly exists. This entanglement is encompassed by a definition that has been posited to describe what is ultimately real: that which constrains thought. During the Middle Ages, this discussion of realism versus nominalism explicitly surfaces, at first addressing questions concerning the omnipotence of God, then gradually moving to questions specifically concerning what can possibly be known.

Realism and nominalism are doctrines which can each be expressed as pertaining to different domains of knowledge. Before comparing the two, I aim to first distinguish the type of knowledge that I will focus on. Nominalism objects to realism on two independent grounds: the existence of universals and the existence of abstract thoughts. Universals are ideas which can be instantiated, either by a particular or by another universal. An example of a universal's being instantiated by a particular would be having the universal of redness instantiated by a red apple. An abstract object, on the other hand, refers to any entity of the mind that isn't found in the material world and doesn't cause anything to happen of its own volition. Under these definitions, universals are not strictly a subset of abstract objects. However, a question one may ask is whether a universal somehow exists within each instantiating particular, or whether it exists independently of them. If the latter is argued, then it could be argued by extension that nominalism's argument against universals is very similar to its argument against abstract objects. For this analysis, I will focus mainly on the domain of universals. One important thing to note is that there are universals which are used to differentiate physical entities merely because everyone has agreed that such distinctions should exist. For example, we humans have created the construct of the pet universal. Classifying an animal as a pet is largely a matter of individual opinion, and if everyone were to agree that keeping pets is wrong, then there would be no more distinguishing any particular animal as a pet. The real battleground in the ideological battle between realism and nominalism (and the domain I will focus on) does not consist in these kinds of agreed-upon universals, but rather in the universals involved in Aristotelian science. These are the universals used to define species, for they are supposed to capture the essence of a material entity, are not subjective, and are supposedly fundamental to providing a complete, empirical description of the universe.

The doctrine of realism, as it applies to universals, relates deeply to the notion that the universe is as it is independently of how humans or other inquiring agents perceive it to be. During the Middle Ages, realism manifests itself in various circles of thought pertaining to Gods omnipotence. According to Thomas Aquinas, God must necessarily have created not only an intelligible universe, but also intelligent beings capable of slowly comprehending the universe through intelligence, thereby approaching the perfection of God. John Wycliffe postulated a God similarly constrained by order in the universe. According to Wycliffe, God could not have created the universe in any other way, for everything in the universe perfectly reflects the universals associated with Gods nature and thoughts, as manifested by what is called the divine intellect. Thus, Gods omnipotence is bounded by the universals, for He cannot create anything outside of what's encompassed by them, nor can he annihilate them.

Aside from explicitly theological subject matter, the claims of realism expand to more explicit ontological and epistemological questions. The claim of realism is that physical entities and properties are both equally existent. Because properties are real whether or not they're instantiated, they take precedence over particulars in providing true knowledge. In essence, a particular possesses a property because it instantiates the universal which corresponds to that property. This means that categories, inasmuch as they capture the essence of material entities, are not arbitrary. Rather, they are discovered and exist outside and independently of the mind. For example, the universal of redness would exist even if there were no eyes to behold and recognize it. Proponents of realism thus believe that, given enough time, human reason can come to know the true classifications of things in the universe through iterative searching, despite individual flaws in human reasoning.

The realist doctrine possesses what could be referred to as a strong metaphysics. The realist doctrine allows one to make true statements about kinds of objects, not just particulars. This, in turn, opens the door to robust deduction and reasoning about groups. Being able to reason about groups allows one to come to possess theoretically unlimited insight into the underlying structure of the universe. Unfortunately, the conditions which contribute to a strong metaphysics also make for a weaker epistemology. When properties are to take precedent over particulars, it takes much more time to discredit bad explanations of the universe which exist in the minds of others. For example, there's a nearly limitless amount of different ways to attribute universals to particulars through classification. Although many errant classifications could be shot down by reason and limited observation, many others would be much harder to argue against in any reasonable amount of time without extensive observation.

Something should also be said for the implications of the realist doctrine on the question of morality. Morality consists of a set of axioms and paradigms for viewing the universe and other people, imposing a kind of order on the analysis of behavior. These are not observable, yet can be used to classify actions and events in a universal manner. Thus, although the realist view does not appear to guarantee the existence of universals which constitute morality, it clearly allows for them to theoretically exist, and argues for their eminence if they do.

The doctrine of nominalism directly questions the realist assertion that universals exist independently of observable particulars. In the theological domain, William of Occam famously argues for a version of Gods omnipotence that is much different from Aquinas or Wycliffe's. According to his view, God is not a being limited by reason; everything in the universe is governed by His divine will, and not His divine intellect. Therefore, if God wanted to create a creature which directly contradicted any currently-held species classification, then He could do so arbitrarily. Such a model of the universe renders any classification of species arbitrary, in turn. Such a view of divine omnipotence naturally leads to a reevaluation of the relationship between particulars and categories.

When properties are rendered arbitrary, physical entities must carry all the weight in leading to truth. Concerning the status of properties and relations, one can either reject the existence of such universals outright or accept them, yet claim that they're not actually universals. As an example of the second option, one could consider the minimal amount of properties, or descriptors, that account for the similarity and causal power of everything in the universe. The nominalist could argue that all of these properties could be expressed entirely in terms of particulars. Surely, this would require a much greater number of particulars to provide an equally broad description of the universe nevertheless, such a formulation would ultimately be no less descriptive. Instead of referring to the redness of all apples of a certain kind, the nominalist refers to the redness of this particular apple, which exists exactly where and when this apple is red nothing more can be reliably said on the matter. No conclusion can be made about its resemblance to other red apples; each must be examined on its own. Universals are not given in observations, yet they are used to make sense of observation show can their veracity ever be totally verified? Full knowledge consists in learning of the particular, and claims about similarity between objects are merely used when one lacks sufficient knowledge or wherewithal to get a good look at the particular. Under this view of universals, any use of classification is purely a pragmatic exercise, at times necessary to make decisions and to act. Classifications can be useful, but they are impositions on reality.

Whereas realism boasts a relatively strong metaphysics, nominalism claims a stronger epistemology. According to the nominalist, to resolve disagreements about the world, one must appeal to something outside of reason: observation of the particulars. Simple observations leave less up to interpretation in fact, ideally, they leave nothing to subjective interpretation. This stronger epistemology comes at the price of a weaker metaphysics. Under the nominalist doctrine, all classifications are man-made, and so one cannot actually speak to the true essence of a thing beyond what is immediately observable. One can identify the essences of sets which are created for pragmatic purposes, such as odd numbers, but never of observable things. Thus, there can be no discovery of universal properties. Constructs such as the laws of physics are not actually laws, but particular behaviors observed at a particular point in time. Broadly, nominalism denies that it is necessary that the universe be governed by order at least in the way that human beings understand order as it arises from interrelation. This pattern is evident in the way that Protestant Reformers come to embrace nominalism, for they come very close to practicing a form of mysticism. Perhaps the only thing keeping Protestants from becoming mystics is their staunch anchoring of their doctrine on both the literal word of the Bible and personal revelation.

Under the nominalist doctrine, the question of morality becomes muddled, as well. If the conclusions from observing an object can go no further in their application than that particular object at that particular point in time, then an is-ought problem arises. By this, I mean that what ought to be can never be concluded from observing what is. Under this paradigm, there are no moral absolutes. Morality becomes purely a pragmatic tool, used for its observably desirable outcomes under certain circumstances, though never logically justified absolutely.

By my own estimation, it appears that it would not be practical to espouse both the doctrine of realism and nominalism simultaneously. The reason has to do with the application of Occam's razor. As mentioned in the description of the nominalist doctrine, one could plausibly conceive of a descriptive duality between properties and particulars. The nominalist could argue that the minimal set of universally descriptive properties could be equally represented by particulars. In this case, all the theoretical roles of universals would be equally fulfilled by material entities. If this were so (it is, admittedly, a big if), then Occam's razor would urge the rational thinker to not unnecessarily multiply the number of entities in the universe. In general, universals rely on their supposed function as proof that they actually exist, and if they were shown to be entirely redundant in their function, then one would be inclined to reject universals altogether for the sake of concision.

I personally find the nominalist viewpoint to be very attractive, mainly because it appears to have built into it a constant call for intellectual humility. I have long been cautious in my estimation of the limits of human reason, and my study of engineering and mathematics has caused me to develop the view that mathematics constitute a useful yet approximate structure for modelling reality. Moreover, the analysis of nominalist philosophers such as Immanuel Kant has opened my eyes to the very real possibility that the way in which we perceive the world is distorted by our particular notions of space and time, which form the backbone of human reasoning. It is also difficult for me to argue against Aristotle's conjecture that categories appear to be existentially dependent on particulars, for it aligns with my intuition that the mind formulates models for the sake of its own survival, and not necessarily for the sake of obtaining absolute truth. Given all of this, however, I realize that there is a big difference between encouraging intellectual humility and throwing out the merits of human reasoning altogether.

Although I cannot claim to be able to prove the supremacy of either doctrine, it seems to me that nominalism leads to a fundamentally unsettling conclusion when taken to its logical end. As a rational thinker, if I were to embrace nominalism as the lens through which to see the world, then I would have to continually reconcile the fact that I have to constantly appeal to immaterial ideas and classifications in order to make any intellectual progress that is useful to me. Supposedly, I could reason about groups, all while viewing it as a purely pragmatic endeavor. But, then, what meaning would the word pragmatic even have? What universal principle would compel me to do what is useful? How could I ever justify a belief concerning what is actually useful? I would be doomed to spending the rest of my life questioning the merits of every thought, and every thought concerning a thought, if I were to hold myself to intellectual honesty. The nominalist viewpoint would destroy any semblance of inner compass that I have if I were to wholeheartedly embrace it. That is why I choose to believe it is more plausible than not that there is a fundamental order to the universe which can, given time, ultimately be comprehended, even if only in part.