Some statements are true, and known to be true, just from the terms that make them up, yet their truth is immediately known from an encounter with their subjects in sense perception. Not only do we come to know universal concepts from sense experience according to Aristotle and Aquinas, but also certain propositions, which are known to be true whenever and because their terms are known. As such, they are self-evident, not because they are innate or implanted in the mind (as Plato and his followers thought), nor mere stipulation (all bachelors are unmarried), nor tautologies (all gifts are free, or all surprises are unexpected), but, as we will see below, because they derive from our immediate contact with reality. The propositions are called first principles, and these may be restricted to certain types of concepts or sciences (“a line is the shortest (set of points in the) distance between two points”), or the common primary principles or axioms (dignitates or maxims). The first kind of self-evident principles are known to the learned, those versed in particular sciences, such as geometry. The latter, common principles are known to anyone who uses their reason (which apparently sometimes people fail to do, as some thinkers have been known to deny these first principles.)
Aquinas distinguishes between immediate propositions whose terms are common or grasped by everyone, which he calls common principles or common conceptions of the mind, and those whose terms are conceived by only some people.[1]
In both cases first principles are not mere concepts but propositions. In this, one might think their consideration belongs to the part of logic dealing with judgment, but both thinkers treat of them briefly in regard to induction.
Aristotle only gives three examples of axioms in Book I, Chapter 5 of his Posterior Analytics, but Aquinas throughout his writings repeats these and adds a fourth. (Commentary on Aristotle’s Posterior Analytics, Book I, Lecture 5, n. 6). Both speak as if there are others, but they do not specify what they might be.
- The Law of Non-Contradiction: “…simultaneous assertion and negation is impossible….” (77a10). Saint Thomas sometimes expresses this as “It does not occur that the same thing is and is not.” Later philosophers have given this principle greater precision as “A thing cannot both be and not be at the same time and in the same respect.”
- Law of the Excluded Middle: “…either the assertion or the negation of every predicate must be true…” (77a22). Saint Thomas sometimes expresses this as “affirmation and negation are not simultaneously true” Every proposition must be either true or false exclusively; there is no third option.
- Law of Equality: “…when equals are taken from equals, the remainders are equal.” (76a40) Saint Thomas sometimes expresses this as “Things equal to one and the same (thing) are equal to one another.” (ST I-II, q. 94, a. 2.) [We use this principle quite often when we measure things against a rule or standard (literally in lengths and weights, and figuratively in ethics and law, among other contexts).]
- Law of Greater Whole: Aquinas also adds to these the first principle, “Every whole is greater than its part.” (Commentary on Aristotle’s Posterior Analytics, Book I, Lecture 5, n. 6, ST I-II, q. 94, a. 2.)
Aquinas also sometimes calls all of these the first indemonstrable principles, since they are not the result of demonstration, but are known immediately and by all people. As indemonstrable, they are not technically scientific, since all science comes from demonstration (as we will see below). They are, however, nevertheless known as necessary, indeed more necessary than demonstrations which depend on them, and thus these principles are necessary for acquiring new knowledge.
First, by virtue of being predications in which the predicate belongs to the account of the subject, they are essential predications and, as such, universally and necessarily true. Second, Aquinas holds that the facts expressed by immediate propositions are such that when we are acquainted with them, we cannot fail to see their necessity; that is, we cannot conceive of the falsity of those propositions.[2]
While Aristotle supposes that induction gives us knowledge of these basic propositions, just as it produces universal concepts, and that somehow, they come about out of a process of greater and greater generalization, he does not explicitly say how this happens. Aquinas gives a somewhat clearer but different account of how these axioms arise immediately in our contact with sensible things.
However, in the case of some of these propositions the terms are such that they are understood by everyone, as being and one and those other notions that are characteristic of being precisely as being: for being is the first concept in the intellect. Hence it is necessary that propositions of this kind be held as known in virtue of themselves not only as they stand [in themselves (per se)] but also in reference to us (quoad nos). Examples of these are the propositions that ‘It does not occur that the same thing is and is not’ and that ‘The whole is greater than its part’, and others like these. Hence all the sciences take principles of this kind from metaphysics whose task it is to consider being absolutely and the characteristics of being.[3]
In sense perception, Aquinas teaches, one first forms a concept of being – being as first known – and immediately (though implicitly) forms true judgements about the being of anything that is, namely that it is, and cannot not be.
For that which, before aught else, falls under apprehension, is being, the notion of which is included in all things whatsoever a man apprehends. Wherefore the first indemonstrable principle is that the same thing cannot be affirmed and denied at the same time, which is based on the notion of being and not-being: and on this principle all others are based . . .. [4]
For Aquinas, the mind first acquires an immediate and basic understanding of reality; it is what he calls being as first known or ens ut primum cognitum based on the actuality of the world with which the intellect has first contact in sensation. In knowing through induction, the kinds of things that are actually sensed, the intellect grasps not only what they are, i.e., the essence or quiddity (see predicaments above) of the things sensed. Rather, for Aquinas what first falls into the intellect is being in the sense of being actually present to the senses, i.e. being “something-there, “as Joseph Bobik puts it,
This vague and confused notion … can only be indicated descriptively by such phrases as: ‘that which is present’; ‘that which is given’; ‘the factual’– and most commonly, ‘that which I can touch and see and smell …’.[5]
What the intellect first alights upon is the fact that its activity is directed toward the actual, real, sensible thing which is actually affecting the sense organ. And from this first contact with reality, the mind intuits, however implicitly, the first principle that a thing cannot be and not be, being based ultimately on the fact that reality is what it is and is not otherwise. This primal or primordial grasp of the being, the actuality of real things, is not identical with the subject of metaphysics (as we will have occasion to discuss in a later chapter of the Overview). For Aquinas, metaphysics is the pinnacle of philosophical sciences, the last to be studied, and the crowning achievement of wisdom to be achieved by natural reason (as opposed to supernatural revelation). For being as first known (ens ut primum cognitum) is grasped implicitly and confusedly, while metaphysics studies being precisely, and with much demonstrative argumentation, as being (ens inquantum ens), having distinguished the consideration of things under the aspect of being from the consideration of them under the aspect of matter and motion. In both being as first known (ens ut primum cognitum) and being as being (ens inquantum ens) or the subject of metaphysics, the mind grasps the same reality; each has the same referent, yet under different aspects, or with different senses.
The first concept which falls under our apprehension is being, and this concept contains in act, although confusedly, all beings, because outside this concept literally nothing exists…. Materially, not formally, the first cognitive notions and the subject of metaphysics are identical.[6]
Aquinas says that our intuition of the axioms is founded upon our first grasp and conception of being, and likewise all knowledge is grounded upon the intuition of the axioms. All reasoning depends upon the apprehension of first principles, and these first principles result from the intellect’s first encounter with reality, i.e. being as it is first known. Therefore, all subsequent knowledge that we attain through reason depends upon our having temporally first encountered reality, and grasped that reality of being that is the primum cognitum. And since this grasp of being is temporally prior to all reasoning, it is also prior to scientific reasoning.
Which propositions are immediate, then depends solely on what real natures there are and what relations hold among them, that is, on the basic structure of the world …. When he claims that the first principles of demonstration must be immediate and indemonstrable, he is claiming that they must express metaphysically immediate propositions ….[7]
[1] Scott MacDonald, “Theory of Knowledge” in The Cambridge Companion to Aquinas, p. 172.
[2] Ibid., p. 171.
[3] Commentary on Aristotle’s Posterior Analytics, Book I, Lecture 5, nos. 6-7.
[5] Aquinas on Being and Essence, (University of Notre Dame Press 1965), pp. 3-10, 43-44. See also Michael Tavuzzi, “Aquinas on the Preliminary Grasp of Being,” Thomist, 51 (1987), p. 571.
[6] Antonio Moreno, O.P., “The Nature of Metaphysics,” Thomist, 30 (1966), p. 122.
[7] MacDonald, art. cit., p. 170.
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