Intellectual knowledge is distinguished from sense knowledge (including imagining) in that intellectual knowledge is somehow of what is universal, e.g. of the nature of triangles rather than of individual triangles. But some philosophers claim that there is no knowledge of universals. Hence the question of whether there is such knowledge must be investigated.

Plato was the first to set out clearly what was later called the problem of universals. In his dialogues he has Socrates ask his interlocutors such questions as, "What is holiness," What is justice," etc. Invariably the other man answers first by giving individual examples: holiness is doing this, or justice is doing that. And Socrates replies somewhat as follows: "I didn't ask you for individual instances of holiness (or justice, etc.); I wanted you to tell me what holiness itself is, i.e., what all things called `holy' have in common." Plato's answer to this problem (or at least, his answer as traditionally interpreted) is called "realism." According to him, many different things are called "holy" because they share in, or participate in, a unitary, pure, nonmaterial form or essence of holiness (and likewise for other things: individuals are called "just" because they share in justice, "triangles" because they share in triangularity, and so on). However, right now we are more interested in the structure of the problem.

Considered in more detail, the problem is this. We call this "just," that "just," and the next action "just." That is, we predicate the same word of many different individuals. The question is: why do we call these actions just, but not any of the other things in the universe? There must be some criterion which guides me so that I call these things "just" but not anything else. Likewise for other examples: I call some things "triangle" but not many other things. Put otherwise: I put some things, but not others, into a certain class, say the class of things called "triangle;" what criterion do I appeal to in order to determine which individuals belong to the class and which do not?

The next point is that it seems that the criterion I use must have some basis in reality. That these individuals belong to the class of triangles, but not those others, certainly seems to have something to do with the individuals in question. My grouping of some things into the class of things called "triangle" does not seem merely arbitrary. Our classifications (or many of them, at any rate) must have some basis in reality.

A further point. The reason why I call this individual a "triangle" seems in some way to be the same reason why I call this other thing a "triangle." That is, the criterion for class membership seems to be unitary for the class in question.

The Platonic or Realist solution is to say that I call many individuals by the same word because each of them shares in the one form or essence signified by the word. For example, many individuals are called "triangle" because each of them shares in pure triangularity, which is what the word "triangle" stands for. Hence on the realist position, there is a qualitative distinction between intellectual knowledge and sense knowledge (including imagination and sense memory). Moreover, for the realist this distinction corresponds to the difference between universals and individuals, and universals as well as individuals exist in reality, independently of thought. That is why this position is called "realism:" it asserts that universals are real, independently of thought. As we shall see in a moment, there is another possible position, often called "moderate realism." It holds that we do have universal concepts (hence it is opposed to nominalism), but that a universal concept represents, not a really existing universal, some feature possessed by many individuals.

The realist is opposed by the nominalist. According to the nominalist, there are neither really existing universals nor universal concepts. The extreme nominalist, of which there are few examples in the history of philosophy, holds that there is no basis in reality for our calling many things by the same word, that our classifications are purely arbitrary or conventional. However, this position is easily seen to be false: it is clear that there is some basis in reality for my calling some things "triangle" but not others--it seems that people from all cultures can learn what is meant by the word "triangle," if they don't already have that classification; and the result is that in a wide range of instances, people from various cultures can agree on what to put into that class and what not to. This would not be so if the classification were purely arbitrary. (Note: this example can also illustrate how classifications can have a degree of conventionality in them, viz., with respect to whether to count this or that feature as an important criterion for classifying. That is, the feature signified by the word "triangle" may not be important to some cultures and hence they may not have a word for it. Yet this fact does not show that those cultures which do have a word for it are not picking out some feature really possessed by many different things and not by others.)

The resemblance nominalist has a more plausible position. According to this position, many things are called by the same word, not because they share in some pure universal, and not because the same nature is found in each, but simply because they have a certain resemblance or similarity to each other. (Hence the name "resemblance nominalism.") So there is, on this position, some basis in reality for the common predication, but the basis is only a similarity.

Often in explaining how we predicate the same word of many individuals the resemblance nominalist uses the notion of paradigms or models. According to the resemblance nominalist, when I call this "red," that "red" and so on, "red" does not mean "possessing redness" or anything like that. Rather, what I do is, first, form an image of a particular, and this image serves as my paradigm or model. Then, I simply call all things similar to my model by the same word. For example, I form an image of a nice, plump tomato. And I call all things similar to it by the word "red." Hence "red" does not mean, "possessing redness;" rather, it means, "similar to a tomato." "Triangle" does not mean, "possessing triangularity," but " similar to ... " whatever paradigm I have in my imagination. In this way nominalists claim there is no need to posit anything like universal concepts, and so that there is no need to posit a qualitative difference between intellectual knowledge and sense knowledge. Human "intellectual knowledge," for the nominalist, is simply a very complicated manipulation of images and words. Thought is not something on a different level than imagination and language.

In sum:

Realism: There are ideas or concepts in addition to sense images. That which our concepts present to us as a universal really exists outside the mind as a universal.

Nominalism: There are no concepts distinct from sense images. Human knowledge does not grasp something held in common by many things.

Moderate Realism: There are ideas or concepts in addition to sense images. That which our concepts present to us as a universal exists outside the mind individuated.

There are several objections to nominalism; two will be considered briefly here. First, go back to the example of "red." Suppose my model image is that of a plump tomato. Then, says the nominalist, I call all things similar to a tomato by the word "red." Well, suppose I am presented with a blue ball; do I call that "red" or not? The blue ball is similar to a tomato. Of course, the clear answer to this is that the blue ball is not similar in the relevant respect; the ball is similar to the tomato with respect to shape but not with respect to color. But that is to reintroduce universals, namely shape and color. In other words, things are similar to each other in many different respects. The criterion for class membership cannot be simply similarity; the respect in which the members of the class are similar must also be indicated, and when one does that one has reintroduced a universal. Resemblance nominalism fails to give an account of predication without resorting to universal concepts.

The second problem is "similar" to the first. According to the resemblance nominalist, x is called "red" because of its similarity to (say) a tomato; y also is called "red" because of its similarity to a tomato; and z also is called "red," again, because of its similarity to a tomato. But, instead of getting rid of universals, this explanation makes use of another universal, namely similar to a tomato, a relational universal. So again the nominalist has failed to explain predication without resorting to universal concepts. If the resemblance nominalist attempts to explain "similarity to a tomato" by its similarity to a model of similarity-situations, he will land in a vicious infinite regress. He will have to say, "x's similarity to a tomato is similar to y's similarity to a tomato." But then in turn he will have to explain similarities to similarities, by a similarity of a similarity to a similarity to a model of a similarity to a similarity, and so on ad infinitum. There will always be a residual universal in his explanation.

So, nominalism fails. Therefore we do have universal concepts. By "a universal concept" is meant: a mental presentation of that which is held in common by many things. Sometimes "concept" refers to the content of such a mental presentation. In a concept we grasp a feature or content that is possessed by many individuals (or can be possessed by many).

To say that we have universal concepts is not the same as to say that what is represented in those concepts exists in the real, outside the mind, in the same way as that content exists in the mind. The first argument against realism is simple. There is no need to posit that a universal humanity (say) exists in the real, corresponding to our universal concept of humanity. Rather, one need only say that our concept isolates (abstracts) a content or feature for consideration that exists in the real in each human being as individuated. In other words, the same content exists as universal (a one common to many) in the mind and as individual (in each human being) in the real. Realism simply imposes the conditions of thought (universality) upon the real. There is no warrant for that imposition.

The second problem is that realism runs into an infinite regress similar to that of resemblance nominalism. Both resemblance nominalism and realism explain x's being red and x's being called "red" through some extrinsic relation, through some relation x has to something outside it. So, according to realism, x is red because it shares in redness, y is red because it also shares in redness, and z is red because it too shares in redness. But then sharing in is something found in many instances, and so the three sharings in must share in the pure form of Sharing In. But now there are three new sharings in, which are different from the first three sharings in, since they are second-order sharings in. So, there must be another pure form of Second-Order Sharing In. And the regress goes on indefinitely, with the result that x, y, and z's being red is never explained. Hence realism also fails to account for predication.

The upshot of this argument is that a thing must be red and must be called "red" because of something intrinsic to it. Neither nominalism nor realism satisfy this requirement. On the one hand, we do have universal concepts, but on the other hand, a concept presents to the mind a feature that is intrinsic to each of the things of a certain class. The concept triangle, for example, is the presentation to the mind of that feature intrinsic to each thing rightly called a triangle. The word "triangle" directly signifies that feature, and thus only indirectly individual triangles.

Our concepts are abstract, and for that reason universal. This section explains this point. Consider two horses eating hay in a field. They differ in many respects. One is brown while the other is white; one is tall and the other is short, etc. When I think horse I leave out of consideration those features, such as color and height, by which those individuals, and several others, differ from each other. I isolate the feature signified by the word "horse" from many others with which it is accompanied in this or that horse in the real world. That isolation is called "abstraction." Hence thought is abstract in character, to the degree that it leaves out of account features by which things are divided from each other. Hence some thought is more abstract than other thought.

But all thought is abstract at least to some extent. All concepts abstract from what belongs to the individual as such. Suppose the two horses in the field are joined by a third, which is exactly like the first in every respect. That is, it is the same in color, in height, in weight, in smell, etc. If they are exactly the same in every respect, how then are they different at all, how is it that they are two horses? Well, if they are two, they do differ at least in this, that the content horse is found in this "chunk" of matter and also in that chunk. That is, they don't differ qua horse, or qua height, or qua any understandable difference, but they do differ in that horse is divided (made two) by matter. Hence to think horse is to abstract from the conditions of matter. Matter is what ultimately sets this horse off from every other horse, it is what makes this horse an individual. On the contrary, abstracting from matter, or material conditions, is what engenders a something one that can be possessed by many, that is, a universal. That is, isolating the feature horse from what makes that content this horse or that one, is precisely what renders that feature universal. This point is what Aristotle and St. Thomas mean when they say that matter is the principle of individuation, and since understanding is of what is universal it follows that it abstracts from material conditions and is an immaterial action.

Although we shall return to this point later, we can note in passing how this understanding of universals begins to make sense of the position, held by Aristotle and Aquinas, that knowledge is a special kind of union between the knower and the thing known. According to Aristotle and Aquinas, in knowledge the knowing power is the thing known, to the extent that it is known. Knowledge is an identity of the knower with the thing known. Or sometimes they will say that in knowledge, "the thing known is in the knower."

This can be understood as follows. When I understand a horse the content signified by the word "horse" exists not only in the real in individual horses, but also in my mind as I consider it. Hence when I form the concept horse I apprehend an understandable aspect of real horses. That is, the intelligible aspect I consider is identical in content with some aspect of real horses. By having this concept I am united with reality. (Note: at the level of concepts I do not yet know that the intelligible aspect I consider is identical with some aspect of real things, I do not yet know that my thought is conformed with reality. That comes in a distinct act; at this point I simply consider the intelligible aspect without adverting to whether it corresponds to reality or not, to whether it is subjective or objective. Yet it is conformed with reality, it is identical with some aspect of a thing or things. It is in the second act of the mind, judgment, that I discover that what I consider is identical with something of the real.)

There are three distinct types of acts of the mind. So far we have only considered the first type. The three acts (discussed more fully in class) are:

(1) Simple Understanding: the grasping of an intelligible aspect of a thing, without asserting or denying anything of it or of the real.

the terminus of this act: a concept--often, though not always, signified by a single word

(2) Judgment: asserting or denying that something is or is so

the terminus of this act: a proposition--usually signified by a sentence

(3) Reasoning: inferring the truth of a proposition as derived from other propositions

terminus: an argument