The problem of universals is an ancient question from metaphysics that has inspired a range of philosophical topics and disputes: "Should the properties an object has in common with other objects, such as color and shape, be considered to exist beyond those objects? And if a property exists separately from objects, what is the nature of that existence?"
Universals are qualities or relations found in two or more entities. As an example, if all cup-holders are circular in some way, then circularity may be considered a universal property of cup-holders.Loux (1998), p. 20; (2001), p. 3 Similarly, if one has a set of seven red and three blue balls, it would seem that though the set comprises ten separate entities (balls), there are only two colors therein—each being shared by multiple balls. Many properties can be universal: being human, red, male or female, liquid or solid, big or small, etc.Loux (2001), p. 4
The problem of universals relates to various inquiries within metaphysics, logic, and epistemology, dating from as far back as Plato and Aristotle, in efforts to understand how the same single property can be (at least apparently) shared across multiple, non-identical objects. Philosophers agree that human beings can talk and think about universals, but disagree on whether universals exist in reality beyond mere thought and speech.
Ancient philosophy The problem of universals is considered a central issue in traditional metaphysics and can be traced back to the philosophy of Plato and Aristotle, particularly in their attempts to explain the nature and status of forms. These philosophers explored the problem through analyses of predication, qualities, and knowledge.
Plato Plato theorized a sharp distinction between the sensible world of concrete objects and the intelligible world of abstract universals or Forms (eide; sg. eidos): one merely has beliefs and opinions about the former, but may obtain true knowledge of the latter. For Plato, it was not possible to have genuine knowledge of that which is changeable and particular, since such knowledge must be forever unfailing and general;MacLeod & Rubenstein (2006), §1b. thus, the world of the Forms is the more real or fundamental world, like objects seen in sunlight, while the sensible world is only imperfectly or derivatively real, like the shadows cast by those objects. This Platonic realism, however, in denying that the eternal Forms are mental artifacts, differs sharply with modern forms of idealism.
One of the first nominalist critiques of Plato's realism was that of Diogenes of Sinope, who said "I've seen Plato's cups and table, but not his 'cupness' and 'tableness'."
Aristotle
Plato's student Aristotle disagreed with his tutor: Aristotle transformed Plato's forms into "formal causes", the blueprints or essences of individual things. Whereas Plato idealized geometry, Aristotle emphasized nature and related disciplines, and therefore much of his thinking concerns living beings and their properties. The nature of universals in Aristotle's philosophy therefore hinges upon his view of natural kinds. Instead of categorizing being according to the structure of thought, he proposed that categorical analysis be directed at the structure of the natural world. He used the principle of predication in his Categories, wherein he established that universal terms are involved in a relation of predication if some facts expressed by ordinary sentences hold.
In his work On Interpretation, he explains that a "universal" is that which may be predicated of many, whereas that which is "singular" may not be. For instance, man is a universal, whereas Callias is a singular; both universals (e.g., a genus, such as "animal", and/or species, such as "man") and singulars may be predicated of an individual man (e.g., Callias is both a man and Callias).
Aristotle elsewhere contends—working, at least initially, from the Platonic principle that what is most universal is also (in some sense) most real—that universals are the proper objects of scientific study: since any given sensible thing is changeable, singular, and not wholly definable, whereas the form or essence thereof is—grasped as a universal—enduring, general, and definite, it is the latter that is apt to serve in causes and explanations (i.e., the sort of knowledge with which scientific understanding is concerned).
For example, consider a particular oak tree: this is a member of a species; it has much in common with other oak trees, past, present and future. Its universal—its oakness—is a part of it; hence, one can study oak trees and learn about "oakness", and, more generally, about the intelligible order within the sensible world. Accordingly, Aristotle was more confident than Plato about coming to know the sensible world; he was a prototypical empiricist and a founder of induction. Aristotle was a new, moderate sort of realist about universals.
Medieval philosophy
Boethius The problem was introduced to the medieval world by Boethius ( – 524), in his translation of Porphyry's Isagoge. It begins:
Boethius, in his commentaries on the aforementioned translation, says that a universal—if it were to exist—has to fulfill several criteria: it must be wholly present in each of several particulars, simultaneously and not in a temporal succession, and in an identical manner in each. He further reasons that universals cannot be mind-independent (i.e., cannot have a real existence), because a quality cannot be both one thing and common to many particulars in such a way that it forms part of a particular's substance, as it would then be partaking of both universality and particularity at once—an apparent contradiction. However, he also reasons that universals cannot be solely of the mind, since a mental construct of some quality is an abstraction and understanding of something outside of the mind; thus, either this representation is a true understanding of the quality—in which case we revert to the earlier problem faced by those who believe universals are real—or, if the mental abstraction was not a true understanding, then "what is understood otherwise than the thing is false."
Boethius' solution to this problem was to propose that the mind is able to separate in thought that which is not, necessarily, so separable in reality; he cites the human mind's ability to abstract from concrete particulars as an instance of this. This, according to Boethius, avoids the problem of Platonic universals being out there in the real world, but also the problem of their being purely constructs of the mind: universals are simply the mind thinking about particulars in an abstract, universal way.
Medieval realism
Boethius mostly stayed close to Aristotle in his thinking about universals. Realism's biggest proponents in the Middle Ages, however, came to be Thomas Aquinas and Duns Scotus. Aquinas argued that both the essence of a thing and its existence were clearly distinct;Aquinas, On Being and Essence, ch. I. in this regard he is also Aristotelian.
Duns Scotus argues that in a thing there is no real distinction between the essence and the existence; instead, there is only a formal distinction.John Duns Scotus, Ordinatio I, d. 3, pars 1, qq. 1–2. Scotus believed that universals exist only inside the things that they exemplify, and that they "contract" with the haecceity of the thing to create the individual. As a result of his realist position, he argued strongly against both nominalism and conceptualism, arguing instead for Scotist realism, a medieval response to the conceptualism of Abelard. That is to say, Scotus believed that such properties as 'redness' and 'roundness' exist in reality and are mind-independent entities.
Furthermore, Duns Scotus wrote about this problem in his own commentary (Quaestiones) on Porphyry's Isagoge, as Boethius had done. Scotus was interested in how the mind forms universals, and he believed this to be "caused by the intellect". This intellect acts on the basis that the nature of, say, 'humanity' that is found in other humans and also that the quality is attributable to other individual humans.
Medieval nominalism
The opposing view to realism is one called nominalism, which at its strongest maintains that universals are verbal constructs and that they do not inhere in objects or pre-exist them. Therefore, universals in this view are something which are peculiar to human cognition and language. The French philosopher and theologian Roscellinus (1050–1125) was an early, prominent proponent of this view. His particular view was that universals are little more than vocal utterances (voces).
William of Ockham (1285–1347) wrote extensively on this topic. He argued strongly that universals are a product of abstract human thought. According to Ockham, universals are just words or concepts (at best) that only exist in the mind and have no real place in the external world. His opposition to universals was not based on his eponymous Razor, but rather he found that regarding them as real was contradictory in some sense. An early work has Ockham stating that 'no thing outside the soul is universal, either through itself or through anything real or rational added on, no matter how it is considered or understood'. Nevertheless, his position did shift away from an outright opposition to accommodating them in his later works such as the Summae Logicae (albeit in a modified way that would not classify him as a complete realist).
Modern and contemporary philosophy
Hegel The 19th-century German philosopher Georg Wilhelm Friedrich Hegel discussed the relation of universals and particulars throughout his works. Hegel posited that both exist in a dialectical relationship to one another; that is, one exists only in relation and in reference to the other.
He stated the following on the issue:
Mill
The 19th-century British philosopher John Stuart Mill discussed the problem of universals in the course of a book that eviscerated the philosophy of Sir William Hamilton. Mill wrote:
However, he then proceeds to, seemingly, concede the existence of abstract universals—at least, insofar as they may be conceptualized—in stating the following:
In other words, we may be "temporarily unconscious" of whether an image is white, black, yellow, or purple, and concentrate our attention upon the fact that it is (e.g.) a man, and upon just those attributes necessary to identify it as a man—but not as any particular one. That which we thus conceive may then have the significance of a universal of manhood.
Peirce The 19th-century American logician Charles Sanders Peirce, known as the father of pragmatism, 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."Peirce, C.S. (1871), Review: Fraser's Edition of the Works of George Berkeley in North American Review 113(October):449-72, reprinted in Collected Papers of Charles Sanders Peirce v. 8, paragraphs 7-38 and in Writings of Charles S. Peirce v. 2, pp. 462-486. Peirce Edition Project Online version. He includes among these paradoxical doctrines Berkeley's denial of "the possibility of forming the simplest general conception", while at the same time "admit[ting] the existence of Platonic ideas". Peirce 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 jogs 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 formula and an idea?
Peirce also held, as a matter of ontology, that what he called "Thirdness"—generalities, laws, general facts about the world—are extra-mental realities.