Platonism in the 20th cent.: metaphysics
Plato’s influence on 20th century metaphysics can mainly be seen in discussions of universals. Some philosophers declare themselves Platonists about universals.
Universals, if there are any, are types or kinds of things (such as the kind olive tree or the word “and” as the common type of its utterances), properties (e.g. whiteness) and relations (such as equality). Conversely, types, properties and relations, if there are such entities, are universals if they are not sets in the mathematical sense or representations in our minds. For neither sets nor our representations (unless they are types of representation) count as universals. The philosophers who accept the existence of universals are called realists. They say that particulars (that is, the things that are not universals) instantiate various universals, e.g. their properties.
There are two kinds of realism. According to realism in rebus, a universal is in the particulars that instantiate it, in the sense that it occupies the same position in space as any such particular, or in the sense that it is a constituent of the particular, or in the sense that universals and particulars jointly comprise the space-time world. According to realism ante res, a universal lies beyond the particulars that instantiate it; universals are not entities of the ordinary, space-time world. Also, the in rebus theory denies, while the ante res one accepts, that there are universals which are not instantiated by anything. Realism ante res is a development of Plato’s theory of Forms. It has been argued (Tooley 1987, chap. 3) that some laws of nature require the existence of uninstantiated universals.
One frequent argument against realism in rebus is that it leads to odd consequences about the position of universals in space. Whiteness must at any moment be in different areas of space, wherever a white object is located. The argument already occurs in Plato (e.g., 131a4–c8). One problem for realism ante res is how we have knowledge about entities beyond the world we see. Plato invoked the theory of recollection, but contemporary Platonists would not subscribe to it.
It seems that most 20th century realists supported the in rebus version. Yet some others declared themselves Platonists. One of them was B. Russell (1967, chap. 9–10). He argues that all white objects (or all just acts) have something in common and this can only be a universal, whiteness (or justice). Alternatively, we could select a white patch and say that anything is white if it has the right sort of resemblance to that patch. But then, we shall have to admit at least one universal, the relation of resemblance, which is exemplified by every pair of white things. It would be useless to say that each pair has its own resemblance. For, then, we would have to consider that all those resemblances resemble one another, and in that way we would be forced in the end to admit the universal of resemblance. But once we have admitted it, it is no longer worthwhile not to recognize the other universals.
Russell also argues that a property or relation is not something inside our minds. The area of Edinburgh bears the relation north of to the area of London. The two areas would bear that relation even if there were no human being and no mind in the universe. Moreover, if whiteness were a thought, it would lack its characteristic universality. For a thought in a mind at a time is not one and the same as any thought in another mind or in the same mind but at another time. So, where is the relation north of? It is not in Edinburgh, answers Russell, nor in London. It is located nowhere; universals have no position in space or time. Yet, in his view, for many universals we have knowledge by acquaintance, that is, the kind of knowledge that, for the rest, we possess just for ourselves and our sense-data (our sensory representations). The reason is that many universals are instantiated by sense-data. He also considers that we have the power to perceive some relations between universals, although that perception is not sensory.
Another philosopher who explicitly endorses Platonic tenets is M. Loux (1978, chap. 5). First of all, he argues for the existence of universals by pointing out that a sentence such as “wisdom is a virtue” or “man is a kind of animal” is true. But, in order for the sentence to be true, the subject must have reference. And its reference can only be a universal (wisdom, man). He then argues that any universal is a necessary being, that is, it exists in all possible worlds. For if e.g. we take the kind man or the red colour (which is a universal), we shall see that there are sentences such as “red is a colour” or “man is a substance-kind”. Such a sentence is a necessary truth, that is, it is true with respect to every possible world, but also its truth requires the existence of the universal that the subject refers to. But, he goes on, for many universals there might be nothing instantiating them; e.g., there might be no red objects, or there might be no human beings. Hence, those universals could exist without being instantiated by anything. Given that, we have no reason not to accept the view that there are also actually universals that are not instantiated by anything (such as the property of being a unicorn). According to Loux, it is that view that characterizes Platonism about universals.
Moreover, Loux argues that any universal not only exists in every possible world, but exists at all times in every possible world that possesses time. Consequently, it is not possible for it to begin existing, nor is it possible for it to cease existing. Loux, however, disagrees with Plato’s view that we cannot perceive a universal by the senses. He considers that we have sense-perception of some universals, such as colours and sounds.
- Loux, M. Substance and Attribute: A Study in Ontology.. Dordrecht, 1978.
- Armstrong, D. Universals: An Opinionated Introduction. Boulder, Colorado, 1989.
- Priest, G. One: Being an Investigation into the Unity of Reality and of its Parts, Ιncluding the Singular Object which is Nothingness. Οξφόρδη, 2014.
- Russell, B. The Problems of Philosophy. Οξφόρδη, 1967 (Πρώτη έκδοση 1912).
- Russell, B. My Philosophical Development. London, 1995 (Πρώτη έκδοση 1959).
- Tooley, M. Causation: A Realist Approach. Οξφόρδη, 1987.