The Problems of Universals and Individuation

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The Problems of Universals and Individuation


Roots in Boethius. Through his commentaries (written circa 504–509) on Porphyry’s Isagoge, Boethius introduced a philosophical concern that became a major topic of discussion in the eleventh and twelfth centuries and re-emerged in the late thirteenth and early fourteenth centuries: the problem of universals, which has its roots in a fundamental disagreement in metaphysics between Plato and Aristotle. Plato believed that the essence of a thing—that which makes the thing the kind of a thing it is—has a separate and more real existence than the thing of which it is the essence. He called these essences eidos, a Greek word that means “kind” or “type” but in relation to Plato’s philosophy is usually translated as “Form” or “Idea.” For example, all dogs are dogs because they share or “participate in” the Form of Dog. The Forms are perfect, immaterial, and universal, whereas the things that participate in them are imperfect, material, and individual. Aristotle, on the other hand, said that a universal essence, or form, is combined with matter to constitute an individual thing, which he called ousia or substance. The form can be thought of in separation from the individual substance of which it is the form, but it has no actual existence independent of the thing. Thus, all dogs are dogs (rather than, say, cats) because they possess the form of dog; but there is no Form of Dog that exists in another world over and above the individual canines.

A Mediating Concept. In his Glosae super Platonem (Glosses on Plato, written circa 1100–1115), a commentary on Plato’s Timaeus, Bernard of Chartres, a Platonist, introduced the concept of “native forms” as a mediator between the completely separate universal Forms and individual things. These native forms, he said, are images of the Forms that interact with matter to create individual objects that imperfectly imitate the Forms. Bernard and many of his contemporaries considered the hypothesis of native forms a way to resolve the differences between the two ancient philosophers, but John of Salisbury remarked that it was a pointless exercise to try to reconcile the philosophies of two dead Greeks who had never agreed while they lived.

Realism versus Nominalism. In the later Middle Ages the two main sides in regard to the problem of universals were Realism and Nominalism. Realism was the claim that universals are real; Nominalism was the contention that they are merely names. Despite their difference of opinion as to whether universals exist apart from individuals, Plato and Aristotle would both be considered Realists in the medieval context because of their insistence that universals do exist. Some medieval Realists, such as Bernard of Chartres in the twelfth century, agreed with Plato that they exist independently, while others, such as Thomas Aquinas in the thirteenth century, were Aristotelian Realists. The Nominalists, whether in the twelfth century or the fourteenth, went one giant step further than Aristotle and said that universals do not exist at all, either separately from individual things (Plato) or combined with matter to form individual things (Aristotle). Only the individual things exist; there are no universal structures that they share. Instead, people recognize similarities among various individuals and use a common word, such as human or dog, to refer to all individuals of that kind. But “human” and “dog” are not names of universals in the same way as “Socrates” is the name of an individual. Perhaps the person who most skillfully defended the notion that all reality is individual is the English logician William of Ockham (circa 1285–1347).

Implications of Nominalism. The implications of the Nominalists’ position are far-reaching. If only individual things are real, then a word such as human is a mere sound (in Latin, flatus vocis) without a reference, and there is no common human nature in which all people share. This metaphysical position raises theological problems. If there is no common human essence, how are all later generations affected by original sin as a result of Adam’s transgression? Furthermore, if there are only individual realities, it follows that the individual persons of the Trinity do not share a “common divine nature,” and therefore there are three gods.

The Necessity of Universals. Humans need to use “universal” or “general” terms in language. In the twelfth century Peter Abelard, who rejected the argument of his teacher Roscelin de Compiegne that a universal is just a word, said that “humanity” is not a thing but a “state” or “condition” and that this condition could serve as the basis for universality without there being any need to argue for the existence of a universal reality. This position is known as Moderate Realism. Despite his rejection of his teacher’s Nominalist views, Abelard was influenced

by Roscelin and has been called a Nominalist as well as a Moderate Realist.

Abelard versus William of Champeaux. In addition to asserting his moderate views against extreme Nominalism, Abelard became involved in a dispute with another of his teachers, William of Champeaux, an Ultra-Realist. William held that one single universal essence is present in every individual of a given kind, and that the differences among individuals are merely accidental. In other words, there is only one “humanity”; Socrates and Plato are modifications of that essence. Abelard responded by saying that if Socrates and Plato were really the same substance, then when Socrates was in one town and Plato in another, Socrates must have been in two places at once. (While this retort may be amusing, scholars such as Frederick C. Copleston have pointed out that in William’s theory Socrates was not in two places at once because the word Socrates refers to accidental modifications of the universal substance, not to the substance itself. It is reasonable, however, to say that the same substance, with different accidents or qualities, was in two places at the same time.) William then changed his mind and said that members of a species are the same not essentially but “indifferently,” by which he seems to have meant they are not the same but only similar. This vague formulation, which Abelard treated as a verbal subterfuge, amounts to an abandonment of Ultra-Realism and a victory for Abelard.

Thomas Aquinas and Roger Bacon. In the thirteenth century Thomas Aquinas offered another Moderate Realist solution. Following Aristotle, he said that universals or essences may be abstracted by the mind from material things or substances, but that they have no being apart from substances. As part of a substance, however, the essence does have objective reality. For Aquinas, as for Aristotle and his other followers, abstracted essences are the means by which one can know individual objects. Like Aquinas, Roger Bacon explained human knowledge of the world by means of a sensible species (image), which represents the material thing itself. The species exists itself and is an image of that thing. Following the Arab philosophers Alhazen (Abu ’Ali al-Hazen ibn al-Haytham) and Avicenna, Bacon argued that the image is processed by the brain through common sense, imagination, fantasy, and memory. He also said that all animals have an internal sense of danger and usefulness. Even brute animals are capable of a kind of intelligence, and the human being has a cogitative sense that connects with rationality to produce human rationality and language. How a sensible image guarantees certain knowledge about an external object is the basic problem of knowledge (epistemology). For example, since people can experience afterimages, optical illusions, and delusions as well as seemingly true direct perceptions of objects in the world, how can people be sure that they are seeing a real, extramental object and not an internal impression, or to put it another way: how can one know if a sensible image provides necessary and certain knowledge of an individual thing in the world?

The Problem of Individuation. In the early fourteenth century John Duns Scotus took a new approach to the problem of species and individual. He argued that individuation, what makes a thing unique, is more important than any sort of general essence or species. He asserted that there must be a special principle of individuation, which he called haecaeity or “thisness.” Whereas for Plato, Aristotle, and Aquinas, knowledge could be only of universals, in Duns Scotus’s view the mind has a direct perception or intuition of the “thisness” of the individual being. The mind does use universals as a means of understanding, and the totality of these universal concepts does objectively represent the world. But such generalizations represent both existent and nonexistent objects; intuitive knowledge of haecaeity alone provides certain knowledge of the existence of objects. The important question for Duns Scotus is not “’What is a universal?” but, rather, “What is it that makes an individual an individual?” How, for example, does common human nature become individuated in different people? Duns Scotus rejected Aquinas’s position that matter, which is inherently unknowable, individuates (that is, that Socrates is Socrates and Plato is Plato because their common human essence takes up different parcels of matter); he also rejected the view that various “accidental” features individuate. He held that only what is determinate and distinct in itself, “thisness,” can individuate. The “thisness” of Socrates makes the human nature in him particular to him, even though human nature is found in all other human beings. Duns Scotus was not a Nominalist; he thought that mental abstractions and common nouns are grounded in a fundamental objective reality.

Ockham’s Response. William of Ockham responded to Duns Scotus’s Moderate Realism with a theory that is purely Nominalist. According to Ockham, everything that exists in the natural world is utterly singular or individual. Thus, there are only individual humans; there is no common “humanity” in which they all share. In Ockham’s radical individualism all traces of objective universality are rejected. There is no need for a special principle of individuation, such as Duns Scotus’s “thisness,” because God created a world of individuals. The mind does construct general or universal concepts; but they exist only within the mind, where they serve as signs that recall images of individuals. In his words: “No universal exists outside the mind of the knower.” In Ockham’s fictive (fictum) theory of general ideas one intuits (perceives) real individual things and then abstractively constructs general concepts.


Frederick C. Copleston, Mediaeval Philosophy (London: Methuen, 1952).

Armand A. Maurer, The Philosophy of William of Ockham in the Light of Its Principles (Toronto: Pontifical Institute of Mediaeval Studies, 1999).

Marilyn McCord Adams, William Ockham, 2 volumes (Notre Dame: University of Notre Dame Press, 1989).

Paul Vincent Spade, ed., The Cambridge Companion to Ockham (Cambridge & New York: Cambridge University Press, 1999).

Katherine H. Tachau, Vision and Certitude in the Age of Ockham: Optics, Epistemology and the Foundations of Semantics (Leiden & New York: Brill, 1988).

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The Problems of Universals and Individuation

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The Problems of Universals and Individuation