Problem of universals
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The problem of universals is a conventional term given to what is in fact a nest of intertwined problems, some within the domain of cognitive psychology, others within that of epistemology, still others within ontology. In other words, this problem involves how we think, how we know, and what are the realities to be known.
But since we must begin somewhere, let us ask: is the idea of a river (a universal) more real than the raging waters of the River Maeander (a particular) at this moment? or less real? or differently real?
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The problem of universals in ancient times
The debate may have begun with Heraclitus, an ancient Greek thinker who said that "we never step twice into the same river." In the time it takes us to move our rear foot forward for that second step, water has continued to rush forward, the banks have shifted a bit, and the river is no longer the same.
Heraclitus is often interpreted as suggesting a skeptical conclusion from this observation. Since nothing ever stays the same from moment to moment, any knowledge we may think we have is obsolete before we acquire it. He might also have been suggesting that names are an artificial way to impose stability on the flux of reality -- by calling this a "river" I pretend that it is one entity. This would make of him the first nominalist.
Much in the philosophy of Plato may be understood as an answer to Heraclitus, especially to the skeptical implications of his writings. For Plato, our intellect can contemplate the same river any number of times, for river as an idea, as a form, remains always the same. There is a sharp distinction between the world of the senses and the world of the intellect: one can only have opinions about the former, but one can have knowledge, justified true belief, about the latter. For just that reason, the intelligible world is the real world, the sensible world is only provisionally real, like the shadows on the wall of a cave.
It must be noted that the Platonic notion of timeless ideas, or forms, isn't confined to universals. Particular terms, too, can be understood as the name of an intelligible form. So although river is a form, Meander is also a form, and "the Meander as it was at noon last Friday" is a form. Even "Heraclitean flux" is a form, and as such fluxlessly timeless! There are paradoxes aplenty here, and Plato himself explored them in a dazzlingly dialectical dialogue, Parmenides.
But at least part of what Plato meant to convey is that River, as a universal, is a timeless idea in which the mutable rivers partially participate, as the material world is an imperfect mirror of the really real world. Plato, accordingly, was the first realist.
His student, Aristotle, disagreed with both Plato and Heraclitus. Aristotle transformed Plato's forms into "formal causes," the blueprints implicit in material things. Where Plato idealized geometry, Aristotle practiced biology, and his thinking always returns to living beings. Consider an oak tree. This is a member of a species, and it has much in common with all the oak trees of generations past, and all those that shall come. Its universal, its oakness, is a part of it. Accordingly, Aristotle was much more sanguine than either Heraclitus or Plato about coming to know the sensible world. A biologist can study oak trees and learn about oakness, finding the intelligible order within the sensible world. Such views made Aristotle a realist as to universals, but a new sort of realist. One might call his view moderate realism.
The problem in medieval times
Islamic scholars preserved a tradition of Aristotelian scholarship after Christendom had largely forgotten him. By the thirteenth century, though, the "reconquest" of Spain was making progress, and bringing back into the consciousness of the Latin literate world the riches of ancient Greek philosophy, as found in the recaptured libraries of Toledo.
Thomas Aquinas made it his personal mission to reconcile Aristotle's philosophy with Roman Catholic faith. As part of this task, in De Ente et Essentia he restated Aristotle's views on essence, or universals.
"This nature" he said, meaning a universal, "has a dual being: one in singular things, another in the soul, and both draw accidents to that nature just mentioned. In singular things it has, after all, a multiple being through the diversity of those singular things. But nevertheless is the being of those things not compulsive for that nature, according to its first consideration, namely the absolute."
In other words, oakness exists in the particular trees, as well as in the soul of the biologist studying them. The "being in the things is not compulsive" in that the form itself, oakness, doesn't change though particular oaks die.
As the middle ages waned and the Renaissance approached, European intellectuals switched their allegiances to nominalism. The new Heraclitus of this period was William of Ockham. "I maintain" he wrote, "that a universal is not something real that exists in a subject ... but that it has a being only as a thought-object in the mind [objectivum in anima]." As a general rule, Ockham disbelieved in any entities that were not necessary for explanations. Accordingly, he wrote, there is no reason to believe that there is an entity called "humanity" that resides inside Socrates. Nothing is explained by that. This method of proceeding has since come to be called Ockham's razor, and it has had a career outside of the problem of universals.
The problem in modern times
George Berkeley, best known for his immaterialism, was also an advocate of an extreme nominalism. Indeed, he disbelieved even in the possibility of a general thought as a psychological fact. It is impossible to imagine a man, unless one has in mind a very specific picture of one who is either tall or short, European or Asian, blue-eyed or brown-eyed, etc. When one thinks of a triangle, likewise, it is always obtuse, or right-angled, or acute. There is no mental image of a triangle in general. Not only, then, do general terms fail to correspond to extra-mental realities, they don't correspond to thoughts either.
Berkeleyan nominalism contributed to the same thinker's critique on the possibility of matter. In the climate of English thought in the period following Isaac Newton's great contributions to physics, there was much discussion of a distinction between "primary qualities" and "secondary qualities". The primary qualities were supposed to be true of material objects in themselves (size, position, momentum) whereas the secondary qualities were supposed to be more subjective (color and sound). But on Berkeley's view, just as it is meaningless to speak of triangularity in general aside from specific figures, so it is meaningless to speak of mass in motion without knowing the color. If the color is in the eye of the beholder, so is the mass.
John Stuart Mill discussed the problem of universals in the course of a book that eviscerated the philosophy of Sir William Hamilton. Mill wrote, "The formation of a Concept does not consist in separating the attributes which are said to compose it from all other attributes of the same object, and enabling us to conceive those attributes, disjoined from any others. We neither conceive them, nor think them, nor cognize them in any way, as a thing apart, but solely as forming, in combination with numerous other attributes, the idea of an individual object."
At this point in his discussion he seems to be siding with Berkeley. But he proceeds to concede under some verbal camouflage, that Berkeley's position is impossible, and that every human mind performs the trick Berkeley thought impossible.
"But, though meaning them only as part of a larger agglomeration, we have the power of fixing our attention on them, to the neglect of the other attributes with which we think them combined. While the concentration of attention lasts, if it is sufficiently intense, we may be temporarily unconscious of any of the other attributes, and may really, for a brief interval, have nothing present to our mind but the attributes constituent of the concept."
In other words, we may be "temporarily unconscious" of whether an image is white, black, or yellow and concentrate our attention on the fact that it is a man. It may, then, have the significance of a universal of manhood.
The 19th century American logician Charles Peirce quite appropriately developed his own views on the problem of universals in the course of a review of an edition of the writings of George Berkeley. Peirce begins with the observation that "Berkeley's metaphysical theories have at first sight an air of paradox and levity very unbecoming to a bishop." He includes among these paradoxical doctrines Berkeley's denial of "the possibility of forming the simplest general conception."
Peirce responded to this paradox in the way that one might expect from a man known as the father of pragmatism. He wrote that if there is some mental fact that works in practice the way that a universal would, that fact is a universal. "If I have learned a formula in gibberish which in any way jobs my memory so as to enable me in each single case to act as though I had a general idea, what possible utility is there in distinguishing between such a gibberish ... and an idea?"
Peirce also held as a matter of ontology that what he called "thirdness," the more general facts about the world, are extra-mental realities.
William James learned pragmatism, this way of understanding an idea by its practical effects, from his friend Peirce, but he gave it new significance. (Too new for Peirce's taste -- he came to complain that James had "kidnapped" the term, and to call himself a "pragmaticist" instead.)
Although James certainly agreed with Peirce and against Berkeley that general ideas exist as a psychological fact, he was a nominalist in his ontology. "From every point of view," he wrote, "the overwhelming and portentous character ascribed to universal conceptions is surprising. Why, from Plato and Aristotle, philosophers should have vied with each other in scorn of the knowledge of the particular, and in adoration of that of the general, is hard to understand, seeing that the more adorable knowledge ought to be that of the more adorable things, and that the things of worth are all concretes and singulars. The only value of universal characters is that they help us, by reasoning, to know new truths about individual things."
Three contemporary realists
There are at least three ways in which a realist might try to answer James' challenge of explaining the reason why universal conceptions are more lofty than those of particulars -- there is the moral/political answer, the mathematical/scientific answer, and the anti-paradoxical answer. Each has contemporary or near contemporary advocates.
In 1948 Richard M. Weaver, a conservative political philosopher, wrote Ideas Have Consequences, a book in which he diagnosed what he believed had gone wrong with the modern world, leading indeed to the two world wars that dominated the first half of the 20th century. The problem was, in his words, "the fateful doctrine of nominalism."
Western civilization, Weaver wrote, succumbed to a powerful temptation in the 14th century, the time of William of Ockham, and has paid dearly for it since. "The defeat of logical realism in the great medieval debate was the crucial event in the history of Western culture; from this flowed those acts which issue now in modern decadence."
Roger Penrose, a distinguished physicist, the author for example of a classic 1965 paper, "Gravitational collapse and space-time singularities," contends that the foundations of mathematics can't be understood absent the Platonic view that "mathematical truth is absolute, extern, and eternal, and not based on man-made criteria ... mathematical objects have a timeless existence of their own...."
Nino Cocchiarella, professor emeritus of philosophy at Indiana University, has maintained that realism is the best response to certain logical paradoxes to which nominalism leads. This is the argument, for example, of his paper "Logical Atomism, Nominalism, and Modal Logic," Synthese (June 1975). Note that in a sense Professor Cocchiarella has adopted platonism for anti-platonic reasons. Plato, as one sees in the dialogue Parmenides, was willing to accept a certain amount of paradox with his forms. Cocchiarella adopts the forms to avoid paradox.
Debate about the problem of universals, in all its senses, is no doubt bound to continue.