Lecture 4: Human Knowledge

In his treatment of human knowledge in the Summa Theologiae, Aquinas spends a good deal of time combating a view that he attributes to Plato and his followers. As Aquinas sees it, Plato confuses the mode of our understanding with the mode of the being of things. Aquinas is careful to locate Plato's view within its historical context, as a response to the position of the early natural philosophers who held either that there could be no knowledge because the objects of knowledge are sensible things, always in flux, or that knowledge is a matter of the physical elements in us hooking up with the physical elements in things (ST, I, 84, 1). Wanting to save the character of knowledge as universal, immaterial, and immobile, Plato posits the existence of a separate order of Forms corresponding to our ideas. Aquinas objects that this fails to salvage knowledge of sensible things, which are singular, material, and mobile, and that it renders the union of soul and body inscrutable. What is missing in Plato is a more radical reflection on the nature of our intellectual operation and its relationship to its proper objects, the natures of sensible substances. More specifically, what is missing is the intellectual operation of abstraction performed by the agent intellect (ST, I, 84, 6). For Aquinas, the intellect is both passive, that is, receptive of sensible things, and active upon them (ST, I, 79, 2-3). Our knowledge of sensible things, which is at first vague and general, is made precise and specific by actively engaging with sensible things, by persistent questioning of them. In this way, what is potentially intelligible becomes actually intelligible.

Technically and precisely, Aquinas states that understanding is the result of the intellect's abstracting the intelligible species from the phantasm, an image of the sensible thing. The language of abstraction can be confusing, if we think of it in physical terms as a stripping away of a material surface to arrive at an intelligible or spiritual core. On this picture, the agent intellect's operation would resemble that of a construction crane, extracting the intelligible species from experience. Abstraction is no such mechanical process. It is an "active power to consider the nature of sensible things without considering their individuating conditions," that is, the conditions that pertain to them as this or that instance and not just as members of the species (ST, I, 85, 1, ad 4). Thus we can consider the nature of a cow while disregarding the fact that this cow is here before us now and has a certain color, weight and so forth. In knowing and defining natural substances, be they human beings or cows, we must include flesh and bones but not this flesh and these bones. The contrast is between signate matter, that is, the concrete matter to which we can point and common matter which is common to all the members of a species. Physics includes common but not signate matter, while mathematics, which treats of abstract forms, excludes both signate and common matter, but includes what is called intelligible matter to account for there being numerically many instances of the same form, for example, triangles, squares, etc. Abstraction thus salvages what Plato's doctrine could not: our knowledge of sensible things.

Two objections against abstraction may be considered at this juncture. First, does not abstraction involve falsity because it confuses the sensible singular with the immaterial universal? One response is that the universal corresponds to the nature of sensible singulars, a nature that is more than singular in that it is shared in by many. The deeper response is that the intellect never attributes its mode of understanding to the thing understood. It was this modal difference that eluded Plato. Second, in spite of what Aquinas says about the orientation of the mind to the sensible world, does he not in practice treat sensible singulars as mere means to universal knowledge, as starting points that are to be discarded once we have abstracted the intelligible species? Aquinas reiterates Aristotle's paradoxical expression: we both abstract from and understand in the phantasms (ST, I, 85, 1, ad 5). The locus classicus for this issue is the article which asks whether we need to attend to a phantasm in every act of knowing, even after we possess the intelligible species (ST, I, 84, 7). By way of support for Aristotle's authoritative statement that the soul understands nothing without a phantasm, Aquinas adduces two arguments. First, if this were not the case, our understanding would not be hindered by damage to bodily organs in which our sense resides. Second, from experience we see that the discovery of appropriate examples and the crafting of illuminating images is necessary for our act of understanding. Thus does the formation of phantasms, that is, appropriate examples, assist the facility of the intellect. The most important reason why we cannot sever the intellect's link to sensible singulars is the requirement of truth: the universal must correspond to the nature existing in singulars. Here we encounter once again that reflective act by which the intellect both knows and knows that it knows. In its reflection, the intellect extends to sense and judges that this singular before it is an instance of a certain natural kind. This sort of judgment occurs whenever we encounter an existing thing, which always presents itself as a "this-such," as both a singular and a bearer of a certain universal nature. There is no such thing as a bare singular. In this act, the intellect grasps the existence of the thing and exemplifies the remarkable cooperation and integration of soul and body, since the same man both knows what he senses and senses what he knows. If we reflect upon the activity of knowing sensible singulars, we can discover the experiential basis for Thomas's seemingly contradictory assertions about the human intellect, namely, that it cannot think without a phantasm and that thinking is an operation that resides in not bodily organ. In the very act of attending to sensible singulars, we apprehend them under a formality that transcends their mere particularity. As Aristotle puts it in the Metaphysics VII, every concretely existing substance is a "this," a singular, and a "such," a bearer of a universal nature. The commonplace act of judging that this singular before me is a tree reveals something not only about the thing known but also about the composite unity of the knower, who both knows what he senses and senses what he knows. In the acts of knowing and judging, we are simultaneously oriented to and independent of sense and singularity.

Here we have yet another illustration of how we come to know our own nature by reflection upon our acts of knowing other things. Thus does Aquinas accent something that Aristotle had merely noted, namely, the intellect's capacity of self-reflection and self-appropriation. With Aristotle, Aquinas describes knowledge as an identity of knower and known, but such an identity is also ascribed to sense in its relation to sensible qualities. Sense, however, does not sense that it senses. Self-reflection, then, is peculiar to the intellect. There is no private "I" or "Ego" for Aquinas, since the intellect, as a potency, is nothing until it is actualized by things. Whatever self there is emerges in the very act of knowing the other-as-other. Emphasizing the identity of knower and known underscores the knowing of the other, but not as other. For the latter, reflection on, and self-possession of, our act of knowing are necessary. This does not entail immediate introspection, but rather a mediated return to self in the very act of attending to things.

In a variety of ways, then, Aquinas underscores the intellect's natural orientation to sensible singulars. Indeed, he makes his own Aristotle's teachings a) that the intellect is a potency made actual only by its interaction with things and b) that knowledge is not by contact of knower and known or by the presence of a similitude of the latter in the former but by an identity of knower and known. Some, however, see in the role of the intelligible species as mediator between intellect and thing an anticipation of the modern suject-object dichotomy. In an article which asks whether the species is related to our intellect as what is understood or as that by which we understand (ST, I, 85, 2), Aquinas insists that the primary object of our knowledge is the nature of sensible things. The species is the means by which (quo) we know things rather than what (quod) we know. Aquinas's language might seem to imply that we first inspect the content of our consciousness and then look to the external world to confirm that the content accurately reflects external things. The most obvious problem with this procedure is that it traps us in an infinite regress. If what we encounter first is always the content of our consciousness, the way things have affected us, then the turn from the species to the world will always be frustrated by the fact that we will once again encounter an image or likeness of what exists outside us. One can see here how the view of Descartes and Locke on the temporal priority of ideas in our coming to know external things quite reasonably generates both Hume's skepticism about whether we can know the external world at all and Berkeley's claim that "to be is to be perceived" (esse est percipi).

Descartes' quest for absolute certitude engendered the peculiarly modern enterprise of philosophical justification through epistemology. The framework for the enterprise is the subject-object split. It sets a mind over here in opposition to a world over there. The question is whether we can get there from here. The task is to justify one's knowledge, to vindicate one's claims about the world in the face of skepticism about whether the mind latches onto the world at all. From the perspective of Aristotle and Aquinas, the modern approach looks awfully contrived and artificial; instead of focusing on human beings actively engaged with things in the world, it offers us an abstract mind trying desperately to find entry into the world. Moreover, reasonable doubts are always local, never global; they are formulated against a set of background assumptions that could never all at once be successfully put in question. If doubt were to become truly global, it would be fatal. At the root of the modern problematic is an assumption shared by Descartes, Locke, Berkeley, and Hume, namely, that what we know first are ideas, not things.

Aquinas nowhere asserts that we know the species and then through it know the thing. In terms of temporal order, the species can be known only after we have known the thing, by a reflective act that may accompany our knowing of things. In that reflective act, we simultaneously know the thing and know that we know it. In the latter, we acknowledge that our intellect has been informed by the nature of the thing. This is congruent with Aristotle's dicta that we know activities by first knowing the objects of those activities. If Aquinas does not anticipate the modern problematic, one might still wonder whether it would not be safer to eliminate the language of species altogether. Would it not be less misleading to speak simply of an intellect and a thing, or better, of an intellect knowing a thing. Why posit the species or concept as a third thing? The response is that the concept is not a thing, but the "informed activity of the intellect as it grasps the thing." Indeed, the Latin term conceptum can have our meaning of "concept" but it can also mean "thing conceived." The latter is more in accord with Thomas's use.

Reading Assignment 

Summa Theologiae, I, 79, 84-87.

Writing Assignment

1. Reflect on the meaning and importance of Aquinas's argument that a phantasm or image is necessary for every act of human knowing.

2. Consider the relative strengths and weaknesses of Plato's account of human knowledge, as Aquinas describes it.

Suggested Reading

Aristotle, Metaphysics, VII

Locke, An Essay Concerning Human Understanding, Book I, chapter 1 and Book II, chapters 1-8

Berkeley, A Treatise Conerning the Principles of Human Knowledge

John O'Callaghan, "The Problem of Language and Mental Representation in Aristotle and St. Thomas," The Review of Metaphysics 50 (1997), pp. 499-541.

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