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The Concept of Truth and the Object of Human Knowledge





Fulvio Di Blasi






First of all, let me thank for the invitation to this Interdisciplinary Seminar on the concept of “complexity” to discuss some aspects of my research. In particular, I was asked to explain—on the same lines of an article I published on the philosophical knowledge of God in Thomas Aquinas (to which anyone who wants a deeper understanding of the subject should refer) [1] —the way in which, according to Aquinas, our intellectual cognition of reality happens, and the sense in which we can speak of an opening to a knowledge of God. Here, in no way I will deal with the so called proofs of the existence of God.

Before getting into the subject, I would like to say that I have learned a lot from comparing my research field with that of physicists and mathematicians. I am persuaded that an interdisciplinary approach is indispensable. Everyone looks at reality from a particular viewpoint, and thus is tempted to consider his own the absolute one, considering the others too simple. In our case, I am sure that a proper philosophical discussion on the concept of truth and on the object of human intellectual knowledge will help the scientist to see with more precision what he himself knows when he asserts something, e.g., that reality is “complex” or “chaotic”, and, in general, what is the truth of scientific concepts.



1. Sensory cognition and intellectual cognition


It is well known that Aquinas begins his philosophical way to God with the question of the self-evidence of God’s existence. For him God is not self-evident to our minds [2] . Now, for our purposes, this means fundamentally that the object of our intellectual cognition is never the idea, the concept, the universal: the very object is instead the bodily reality we have in front of us and we know through our senses.

First of all, we should recall that the main difference, at least at a first glance, between the sensory cognition of material things and the intellectual cognition in itself is that in the first case the object is always a particular thing (e.g., the individual dog we have, now and here, in front of us) while in the second the object is always universal (e.g., the concept, the idea, of the dog). So that our way of thinking about reality is different from the way in which reality falls under our senses.

This is the problem of the universals, that we can better express by asking the following question: where do the universals that we have in mind and by which we think about everything, come from? There are, generally speaking, two possible answers. (1) On the one hand, you could say that the universals come somehow from the particular material things. In that case, of course, the central question will be: «how could it happen?». (2) On the other hand, you could protest that, being the material things particular or individual, the universals can by no means come to our minds from bodily reality. This kind of answer raises at least two central questions. (a) The first and the more immediate one is: «if the universals do not come from our sensory cognition, where do they come from?». (b) The second one is more subtle but obvious as well: «if our intellectual cognition does not come from our senses how can we say, in whatever reasonable way, that we know the things?».

The alternative answer to “the universals question” is exemplified by, respectively, Aristotle and Plato. For Plato our intellectual (universal) knowledge can not come from reality (particular), above all because what is known must be actual (actu) with regard to the relevant cognitive faculty; just as “hearing” can know nothing if there is not here and now some actual sound, so the intellect can not know anything if there is not, actually before it, a universal idea. Notwithstanding, says Plato, our intellectual cognition is real because there exists another reality, made of universal, immaterial and unchangeable ideas, from which the material things were shaped as from moulds, and which we knew directly before this life. So we know the material reality by remembering the ideas. In Plato’s thought, therefore, the very object and point of departure of our intellectual knowledge is not the world as we see it but the idea that we remember from our preceding life.

On the contrary, for Aristotle, our intellectual cognition comes from reality by abstracting its intelligible aspects; the ideas, therefore, do not exist in themselves in some other world but they exist only in our intellect as logical objects. Aristotle, of course, recognises that simpliciter the object of the intellect is universal, and that it must be actual to be known. But our intellect, he explains, can in a first stage move itself towards reality in an active way (intellectus agens) abstracting the intelligible forms from the particular things, and so making actual the universal objects which in a second stage it receives in a passive way (as “hearing” receives sounds). According to the Aristotelian gnosiology, therefore, at the beginning of our intellectual cognition there are not ideas but only the material reality we grasp through our senses.



2. Aquinas’s criticism of Plato


Taking the side of the Aristotelian philosophical realism, Aquinas criticises Plato on two counts which we can summarise as follows. (1) The idea in itself is unchangeable and not material. So, if our intellectual cognition begun from ideas we could not know the proper object of natural sciences (which is moving and changeable and material), and we could not know the scientific proofs which start from the moving and material causes. (2) Even if we knew the ideas as separate entities, logically we could not make any assertion on bodily reality. And it is very strange [derisibile videtur] that in order to know the reality that is evidently in front of us, we appeal to other entities essentially different from that reality (as the universal, unchangeable and immaterial differs from the particular, changeable and material) [3] .

In the Platonic position, says Aquinas, the truth would be merely what it seems to each individual, because our intellect would know only its own impressions and it could judge only on them. Science could not have as its object the real things which exist outside the soul.

This last point is the central one, from Plato to Hume, Kant... and Popper, Kuhn, etc.:..  If reality is not intelligible in itself, and our intellectual knowledge does not come from reality, as a matter of logic we can never say anything about reality. The «hypothetico-deductive method», as elaborated by Popper, does not rely primarily upon «empirical observation or induction» from experience but only on «sheer inventions in the minds of the scientists» [4] . And this very fact determines the fundamental weakness of both the «verification» and «falsification» procedures for scientific discoveries. If real events do not, in any way, cause scientific theory, those same events can not logically decide later about its truth or falsity. After Popper, Kuhn will consistently conclude that the transition from one scientific theory to another (i.e., from one idea about the structure of the world to another one) is nothing but the result of a «scientific revolution» [5] .

For Aquinas the idea can not be the basis of our knowledge: it is not reliable because it changes from person to person, and in the same person from moment to moment. It marks, shows, indicates always and constantly the relationship between the knower (the subject who knows) and the reality he knows, according to the measure and the degree of knowledge that he actually has (actually as opposed to potentially).

The concept (idea) is, in this sense, always intentional: it tends towards reality, and it is a constant product of experience, that is to say, of our contact with the world. To know, and to know with certainty, we must relate again and again our ideas, concepts or scientific hypotheses (which are in a very relevant sense the products of the qualified experience – i.e., of the contact with the world – of the scientists) to the reality that exists before us, and, by reasoning, we must improve again and again our knowledge (i.e., intellectual knowledge) of that reality.



3. Proper Object, Object of Second Intention, and Common Object


On the basis of Aquinas’s own gnosiology we have to distinguish between three kinds of objects of human intellectual knowledge: (1), the intelligible species abstracted from the phantasm (object of second intention), (2) the material thing itself, the “res” (quidditas rei materialis – proper object, and object of first intention), and (3) the ens in universali (common object).

The first one, says Aquinas, is the object of the intellect because it is what actually exists in the intellect as the product of the basic abstraction process from the particular things, which fall under our senses. However, he continues, it is not «the proper object» because it is not what we actually think of, id quod actu intelligitur. The first and proper object of our thinking is rather the material thing itself. The idea (the intelligible species) is instead «the means» by which our intellect knows, thinks of, the reality.

It is only in a second phase that, being our intellect capable of returning over itself (re-flecting), we can think our own thinking, that is, the ideas used to know reality: «Sed quia intellectus supra seipsum reflectitur, secundum eandem reflexionem intelligit et suum intelligere, et speciem qua intelligit. Et sic species intellectiva secundario est id quod intelligitur. Sed id quod intelligitur primo, est res cuius species intelligibilis est similitudo» [6] .

The essences of material things are therefore the objects of the intellect, but they are an object of «second intention». The «first intention object» is the bodily reality itself: what we primarily think of, and know, in the constant existential contact with reality.

What now about the common object? There is a sense wherby our intellect has as its object, not the essences of particular things, but the ens in general, in universali. For ens means id quod est, and whatever we think “is” and is “something”; so that every concept we have presupposes the notion (i.e., our previous knowledge of the notion) of ens.

Aquinas explains this point at the beginning of his important work De veritate, saying that everything our intellect conceives turns into the notion of ens, so that all the other concepts must be elaborated by adding something to that notion. Ens is therefore the first thing in our intellectual knowledge: «quod primo intellectus concipit quasi notissimum et in quod conceptiones omnes resolvit est ens... unde oportet quod omnes aliae conceptiones intellectus accipiantur ex additione ad ens» [7] .

Ens, still, is not a generic notion but an analogical one, because there is nothing that can be extraneous to it (everything is something). Thus the other notions are not obtained by adding something to ens as the difference is added to the genus (e.g., man = animal/genus + rational/specific difference), but rather by expressing a way of being not expressed explicitly by the notion of ens: «sed enti non possunt addi aliqua quasi extranea per modum quo differentia additur generi vel accidens subiecto, quia quaelibet natura est essentialiter ens, unde probat etiam Philosophus in III Metaphysicae [8] quod ens non potest esse genus; sed secundum hoc aliqua dicuntur addere super ens in quantum exprimunt modum ipsius entis qui nomine entis non exprimitur» [8] .

The notion of ens (i.e., of being something), finally, is not a simple one. On the one hand, it refers to a particular way of being as it differs from the way of being of all other things. On the other hand, it expresses the being that is common to all things. The notion of ens, in other words, is made up by those of being (the common factor) and essence (the differentiating factor).

Let me emphasise now three consequences of Aquinas’s realistic gnosiology.

(a) The first one, already discussed, is that the measure of human intellectual cognition is always the sensory reality; the ideas, as means toward knowing, vary from person to person and in the same person from time to time.

(b) The second one is that the intellect can not think anything without the actual mediation of images (not only visual) [9] . The reason is that the ideas do not exist in themselves but only as the intelligible forms of particular material things. Thus, even in our mind, they are necessarily linked with the images we receive through the five external senses. Aquinas underlines, on this subject, that we can not think anything without the help of memory and imagination (i.e., without the faculties which have physical images as objects), and invites us to do the very interesting experiment of trying to think of any concept without forming a physical image of it, no matter how vague, indefinite or deformed it is [10] . Even when we think about a scientific concept such as chaos, we create an image of it that is essentially different from the concept but necessary in order to think of it.

(c) The third and last consequence is that we do not realize everything we know (intellectually). That is to say, we do not have all our intellectual cognition of reality (our ideas) as a second intention cognition. With regard to this phenomenon, Finnis offers an evocative example: «We often say “Too late!”; but how often do we formulate the presupposition on which our conclusion rests, the guiding presupposition that time cannot be reversed?» [11] .

With regard to the question of God, the above three consequences hold great importance to avoid misunderstandings and underevaluations of Aquinas’s own view. For him it is clear, in this respect, that the natural knowledge of God is different for everyone, unimaginable, and not necessary reflexive (where reflexive means “of second intention”) [12] .



4. The Concept of Truth


Let us go now to the concept of truth, which is a very useful one to deepen and summarize, at the same time, our understanding of the previous discussion about the object of intellectual knowledge. Here, the main distinction we have to begin with is that between the logical truth (truth simpliciter) and the ontological truth (truth secundum quid).

Truth, says Aquinas, does not concern primarily reality but intellect. We do not say, for instance, that “the dog is true”, but rather that our own assertion or judgement [13] “the dog is near us (or exists or is a sheep-dog)” is true or false; and the measure of our judgement can be nothing if not the effective reality concerning the dog. So, our intellect (our idea) will be true if the dog is really near us; otherwise it will be false. The truth is therefore, first of all (i.e., simpliciter) the logical truth: the truth which belongs to the judgement (i.e., to our ideas), and which expresses always a relation of conformity between “a knower intellect” and “a thing known”. Just from this the proper notion of truth was expressed by the very famous formula «adaequatio rei et intellectus».

Now, because of the intentionality of our knowledge, the adaequatio of the intellect will be true, not when it says all about the thing known, but when it expresses something of it, no matter how much, that really belongs to it. The child’s knowledge of the elephant can be limited to the fact that the elephant is bigger than the dog, while the scholar’s knowledge is more detailed than the layman’s, yet both will be true if they express a real (true) property of the elephant.

It is only secundum quid (under a certain respect) that, in a second phase, we can speak of the truth of the things in themselves (verum: ontological truth), thus making reference to their “real being” as far as it is the object and measure of intellectual knowledge.

This is evidently the sole way you can speak of truth, because even someone who denied this notion would have to adduce that it (as a judgement on the notion of truth) does not really conform to what we really mean to be the notion of truth. This notion does not involve that reality is in some way static or unchangeable, but only that it is always the measure by which man judges his own judgements. So, the historian’s opinion on the régime’s change induced by the French Revolution is more or less qualified as far as it conforms to the real facts, reasons, etc. The statesman’s opinion on the best form of government must be supported by (i.e., must conform to) the facts. And someone who asserts that nature changes has to measure his judgement with the real changes observed, and hence he asserts, in this way, an intelligible feature of reality: e.g., the natural evolution law. Even judgements on chance, or on complexity and chaos, fall within our notion so far as they express, in an intelligible (i.e., in a universal) way, (a) our incapacity to find the explication of some or all the natural phenomena (chance), or (b) the scientific interpretation of a very special phenomenon, e.g. the existence of non linear systems (complexity), and of special cases of non linear systems (chaos).

The notion of logical truth as «adaequatio rei et intellectus» is valid also when it is not the intellect that conforms itself to reality (theoretical truth: adaequatio intellectus ad rem) but, vice versa, it is reality which conforms itself to the intellect (practical truth: adaequatio rei ad intellectum). For the truth of human actions is the conformity with the idea that the agent wants to realize. The measure of practical truth is therefore the agent’s end: both in the praxis, where the end is immanent to the subject, and in the poiesis, where the end is external. Practical truth, finally, depends on theoretical truth because it presupposes in the agent’s mind a previous idea on what reality is and on how it can be changed: in this sense, the best action will be the best one based on nature.



5. Three Kinds of Concepts Our Intellect Produces


It should be clear, by now, the sense according to which, for Aquinas, the ideas (the intelligible species) intuitively [14] abstracted from material things are the object of intellectual cognition. And it should be clear enough, from this, that the main function of our faculties of judgement and reasoning is that of deepening again and again our knowledge of the reality that our senses put immediately in front of us (just that reality of which we can have images in our minds).

But things are indeed more complex, because judgement and reasoning create and improve continuously also new concepts or ideas. Thus, generally speaking, we can distinguish at least three kinds of concepts that our intellect produces in its continuous contact with reality: (1) real and immediate; (2) real but mediate; and (3) fanciful or purely hypothetical. “2” and “3” are new concepts, that is, concepts created by disassembling and reassembling in another way the concepts (and the images) we have immediately from our first intention object.

In the last case (3), for instance, our intellect can create the ideas of “flying horse” and “fairy”, or it can hypothesize the existence of other dimensions, aliens from outer space, or ghosts. In doing so, the intellect must necessarily use images and concepts belonging to the immediately evident bodily reality (wings, horses, dimensions, living beings, etc.), but logically it can not conclude for the real existence of the objects of the new ideas: at least up to the time in which it will find some real signs such to pass from fancy (flying man), or from pure hypothesis, to scientific hypotheses or, directly, to reality.

On the contrary, in the second case (real but mediate) the new ideas will involve necessarily real existence judgements, because they will be coined just in the effort of deepening and better understanding the existing reality. So the ideas of atom, energy, electro-magnetic wave, law of gravity, chaos, etc., are neither fanciful nor purely hypothetical. They can be the result of a mistaken explanation, but their reality remains that of the existing phenomenon they try to rationally understand: the structure of physical objects, the fall of gravies, the transmission of messages on air, the light, the complexity of things, etc.

The concept of truth can be analogically applied to every kind of new ideas. So, the truth of fanciful or purely hypothetical ideas is their mental existence; or, in other words, the truth of our judgements about the fanciful or purely hypothetical ideas rests on our own ideas of them. But the truth of the real but mediate ideas is always the real existence, that is to say, that feature of bodily reality they want to express. Of course, even the pure hypothesis can become an attempt to explain reality if we link it with some real events we know (think, e.g., of the idea of flying man in the last century).

The idea of God, for Aquinas, is a real but mediate one. It varies from person to person and from time to time, it is unimaginable, and it is not necessarily of second intention (at least not according to all its features). But it wants to be an explanation of the existing reality under a very special respect: that of its being in itself, to which the intellect is constantly open because of its common object [15] . Just in this sense, the famous five ways to the existence of God are not “a-priori” but “a-posteriori”: that is to say, they have as their starting point the sensory reality, and not the ideas.




[1]   F. Di Blasi, La conoscenza naturale di Dio in Tommaso d’Aquino, «Aquinas» 2 (1999).

[2]   See, T. d’Aquino, Summa theologiae, I, q. 2, a. 1.

[3]   See, ibid., I, q. 84, a. 1 c.

[4]   Cf, H. B. Veatch, Human Rights. Fact or Fancy?, Baton Rouge, La. 1985, pp. 227-36.

[5]   Cf, K. Popper, The Logic of Scientific Discovery, New York 1961; T. Kuhn, The Structure of Scientific Revolutions, Chicago 1970.

[6]   T. d’Aquino, Summa theologiae, I, q. 85, a. 2.

[7]   T. d’Aquino, De veritate, q. 1, a. 1 c.

[8]   Ibid.

[9]   See, E. Gilson, Introduzione alla filosofia cristiana, Milano 1982, pp. 58-69.

[10]   Cf, T. d’Aquino, Summa theologiae, I, q. 84, a. 7 c; q. 86, a. 1 c.

[11]   Cf, J. Finnis, Natural Law and Natural Rights, Oxford 1980, p. 64.

[12]   On the pre-philosophical knowledge of God, see, A. Livi, Filosofia del senso comune, Milano 1990.

[13]   The judgement is a link between concepts.

[14]   In Aquinas’s gnosiology the knowledge of ideas happens always by intuition. In this respect the function of judgement and reasoning is that of improving again and again our intuition of ideas.

[15]   Cf, C. Fabro, Dall’essere all’esistente, Brescia 1965, pp. 60-9.