Thomas Aquinas on Knowing the Essences of Material Substances

Abstract

Thomas Aquinas on Knowing the Essences of Material Substances Benjamin M. Block I. The Difficulty of Attaining Knowledge of Essences of Substances A CONDENSED OUTLINE of Thomas Aquinas’s explanation of how we attain intellectual knowledge might be expressed as follows: the activity of the agent intellect, using the phantasm as its instrument, produces impressed intelligible species in the possible intellect, which in turn forms its own concepts, or expressed intelligible species, through which it knows the natures of things, in a universal manner.1 Much study would be required before one could even begin to unpack the carefully thought-out details that have been worked out in the above description, but in what follows, I wish to begin by first taking for granted the whole Thomistic epistemological doctrine thus outlined. Given this explanation, the problem that I here propose to solve is how it is possible to provide human beings with a knowledge of the essences of material substances.2 For if it is [End Page 87] true that all human knowledge has its origin in the senses3 and that the senses provide likenesses only of accidents,4 then it is unclear how the agency of the intellect, together with the agency of the phantasms, would be at all sufficient to produce any likeness of a material substance’s essence, for the production of the likeness of a substance’s essence from the likeness of mere accidents seems to be producing something from nothing.5 And yet, Thomas clearly states that the proper object [End Page 88] of the human intellect is the quiddity (or essence) of a material thing, and he further maintains that our intellect cannot fail in its understanding of this object.6 Before attempting to resolve this problem, I want to emphasize its importance briefly, lest unavoidably technical details fool us into thinking of this problem as merely an esoteric exercise in understanding medieval terminology. The question of how we know the essences of material beings lies at the heart of all our questions about what we can know in this life and thus touches directly on questions of man’s purpose and final end.7 When I see, touch, or otherwise experience something— [End Page 89] for example, a dog, a plant, a rock, the moon, another human person—how is it that I can claim that I really know anything else besides my own ideas and my own conscious activities? Perhaps indeed it might seem more reasonable to say, together with John Locke and other so-called empiricists, “Since the mind, in all its thoughts and reasonings, has no other immediate object but its own ideas, which it alone does or can contemplate, it is evident, that our knowledge is only conversant about them.”8 We should here remember that Locke, like Aristotle and like Thomas, also claims that all our knowledge originates from our senses. It is precisely in how Locke and other empiricists understand this process of knowing to take place that leads them to fundamental and far-reaching disagreements with the long-held tradition of perennial philosophy.9 [End Page 90] In contrast, Thomas Aquinas thinks that we really can attain actual knowledge of things, not just of our own ideas, and things are knowable only in their natures or essences.10 Following Aristotle, Thomas further thinks that it is manifest by experience that what we know first, prior to our ideas, is precisely this “external,” material world, and it is this very fact that must be explained by our epistemology; in typical Aristotelian fashion, Thomas does not wish to explain away what is more manifest by what is less manifest.11 But merely positing our knowledge of things as a starting point by no means removes the question of how this knowledge is possible, and because the difficulties involved in understanding this question are indeed great and intricate—especially for those who, like Thomas, hold that all knowledge originates in the senses—the temptation to turn away from a natural realism remains an ever-looming danger. All the more so then, the question of how Thomas thinks it is possible to know...