Foundationalism is, generally speaking, the belief that a group of undoubtable beliefs 'ground,' or 'justify' other beliefs.

As of late, foundationalism has fallen out of favor in many different circles of thought.

At first blush Aquinas seems to be a foundationalist of the sort prone to modern skepticism. But is this right?

To be sure, Aquinas expressed what he felt was a need for 'first principles.' But something tells me they didn't act the same way as they did in a Cartesian epistemology, both a.) because Aquinas never suffered the Cartesian fear of universal skepticism and b.) Aquinas had a radically different epistemology and understanding of how the person comes to know themselves and the world around them (he wouldn't fit into the modern circle of 'rationalism' (undoubtable, a priori propositions found all beliefs) or 'empiricism' (sense-datum found all beliefs)).

Has anyone done some research into this question? Is my suspicion right or way off point?

  • Foundationalism is not confined to Cartesianism, thinkers as different as Plato and Epicurus, Leibniz and Mach were foundationalists, they just differed on what provides the foundation, rational intuition or sense data. Aquinas was an Aristotelian, and despite some innovations his ontology and epistemology are basically Aristotelian. So they have the same problems with "objectively" conceptualized world and givenness of perceptions as all other forms of metaphysical realism.
    – Conifold
    Commented Oct 18, 2017 at 23:42
  • To be fair though we have to distinguish between two semi-overlapping uses of "foundationalism." One usage is for Descartes and Locke and then the rationalists and empiricists who see one thing as the foundation (= source) of truth. Aquinas isn't one of those as he's an Aristotelian. But in a second sense, if "foundationalist" is taken more expansively, every realist position is probably somehow foundationalist.
    – virmaior
    Commented Oct 19, 2017 at 9:36
  • @Conifold As far as I know Aquinas didn't take sense perceptions to, of themselves, ground any proposition. In fact, that's why he postulated, with Aristotle, the need for the 'active intellect.' Depending on the answer to my question, what Aquinas's position might offer is a transcendence of the claustrophobic divide between 'givenness' and 'non-givenness,' a sort of givenness that nevertheless filters through human action, or, contrarily, a human action that is nevertheless informed.
    – user28843
    Commented Oct 19, 2017 at 17:37
  • @virmaior I think you're right. There's definitely two connotations to 'foundation.' One is the post-Cartesian emphasis on undoubtable propositions (be them rationalistic or empiricist) especially as reactive to the threat of skepticism. The other is more concerned with a realist explanation of the origin of our concepts, which may or may not fall into one of the former foundationalisms. Aquinas might have thought that there were certain, undoubtable first principles but these principles originated in our knowledge in a pretty complex way. I'm wondering how Aquinas envisioned this process
    – user28843
    Commented Oct 19, 2017 at 17:47
  • ... And especially how this process informed Aquinas's possible 'foundationalism' in the first sense.
    – user28843
    Commented Oct 19, 2017 at 17:50

2 Answers 2


St. Thomas follows Aristotle in his solution of the regress problem: There must be an indemonstrable first principle because if everything were demonstrable, there would be an infinite regress; cf. his Expositio Posteriorum lib. 1 l. 7. Also, St. Thomas discusses in ibid. l.8 that circular demonstration ultimately leads to saying "if A is, A must be—a simple way of proving anything."

In Summa Theologica I-II q. 94 a. 2 c., St. Thomas states that

the first indemonstrable principle is that "the same thing cannot be affirmed and denied at the same time" [i.e., the principle of non-contradiction] which is based on the notion of "being" and "not-being": and on this principle all others are based, as is stated in Metaph. iv

primum principium indemonstrabile est quod non est simul affirmare et negare, quod fundatur supra rationem entis et non entis, et super hoc principio omnia alia fundantur, ut dicitur in IV Metaphys

Why is the principle of non-contradiction indemonstrable? Commenting on Aristotle's Metaphysics, St. Thomas writes (Sententia libri Metaphysicæ lib. 4 l. 6 [607.]):

[Aristotle] says, first, that certain men deem it fitting, i.e., they wish, to demonstrate this principle [of non-contradiction]; and they do this “through want of education,” i.e., through lack of learning or instruction. For there is want of education when a man does not know what to seek demonstration for and what not to; for not all things can be demonstrated. For if all things were demonstrable, then, since a thing is not demonstrated through itself but through something else, demonstrations would either be circular (although this cannot be true, because then the same thing would be both better known and less well known, as is clear in Book I of the Posterior Analytics), or they would have to proceed to infinity. But if there were an infinite regress in demonstrations, demonstration would be impossible, because the conclusion of any demonstration is made certain by reducing it to the first principle of demonstration. But this would not be the case if demonstration proceeded to infinity in an upward direction. It is clear, then, that not all things are demonstrable. And if some things are not demonstrable, these men cannot say that any principle is more indemonstrable than the above-mentioned one.

Dicit [Aristoteles] ergo primo, quod quidam dignum ducunt, sive volunt demonstrare praedictum principium. Et hoc propter apaedeusiam, idest ineruditionem sive indisciplinationem. Est enim ineruditio, quod homo nesciat quorum oportet quaerere demonstrationem, et quorum non: non enim possunt omnia demonstrari. Si enim omnia demonstrarentur, cum idem per seipsum non demonstretur, sed per aliud, oporteret esse circulum in demonstrationibus. Quod esse non potest: quia sic idem esset notius et minus notum, ut patet in primo posteriorum. Vel oporteret procedere in infinitum. Sed, si in infinitum procederetur, non esset demonstratio; quia quaelibet demonstrationis conclusio redditur certa per reductionem eius in primum demonstrationis principium: quod non esset si in infinitum demonstratio sursum procederet. Patet igitur, quod non sunt omnia demonstrabilia. Et si aliqua sunt non demonstrabilia, non possunt dicere quod aliquod principium sit magis indemonstrabile quam praedictum.

(This answer incorporates parts of this answer and this forum post; cf. this post.)

Courtesy GLeNotre's answer, here's:


Eleonore Stump tries to extricate Aquinas from the Cartesian problematic of foundationalism in this article, "Aquinas on the foundations of knowledge". https://philpapers.org/rec/STUAOT-3

One author who cites Stump wrote an article called "Is Aquinas a Foundationalist?" https://philpapers.org/rec/WILIAA-11

I think the way you phrase what foundationalism is (the belief that a group of undoubtable beliefs 'ground,' or 'justify' other beliefs.) makes Aquinas not a foundationalist, because the first principles are not matters of belief. They are not even Aristotelian endoxa, which is arguably a version of belief.

First principles of demonstration (including the PNC) and first principles of definition (common notions) are perfective states of mind (intellectual virtues) known as understanding (intellectus, nous). It is true that they are at the foundation, because they are starting-points, that is, indemonstrable principles, which precede any definition or demonstration, but we intuitively know them by induction and know them with even more certainty than anything else. So they're definitely not objects of belief.

  • If you're familiar with Wittgenstein, would you say that such 'first principles of demonstration' that don't properly count as 'matters of belief' are similar to Wittgenstein's understanding of foundations of knowledge as being themselves not really 'knowledge' but rather the starting points necessary for knowledge? Or would you say that the first principles are a sort of knowledge that is, nevertheless, not a 'belief'?
    – user28843
    Commented Oct 26, 2017 at 18:53
  • Williams, A. N. “Is Aquinas a Foundationalist?New Blackfriars 91, no. 1031 (January 1, 2010): 20–45. DOI:10.1111/j.1741-2005.2009.01313.x.
    – Geremia
    Commented Oct 30, 2017 at 18:46

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