A Thomistic take on Cogito ergo Sum

The cogito is true. So what is a Thomist to do with it?

Notice that to say that the cogito is true is not to say that everything that Descartes does with it is true, or even that Descartes understands his own axiom in the most fruitful way. But the statement itself is indubitable, and with a long history of precedents. Its indisputable character is such that it clearly deserves to be taken as some sort of first axiom. But how are we to move forward from it?

Descartes valued the certitude of the axiom the most. Here St. Thomas would want to arrange the diverse senses of certitude or certain or sure, and he would insist on certainty or sureness belonging to things first, before the intellect. To be sure or certain is to be determined (more or less) to one outcome or result, and we can know this first of things before our own thoughts. The degree to which we can judge correctly about such determination is part of the question that gives rise to the cogito, but it is still in things that we first find the greater or lesser determination of outcomes.

St. Thomas would be more likely to take the cogito as manifesting something about existence or being, namely, that being is known first – and in an indubitable way – by our own reflection on our vital actions, and in the higher such actions before the lower ones. The most illuminating thing about the cogito when taken in this way is that is shows that existence is innermost in things. In seeing that one thinks, and therefore that he exists, existence is seen as the foundation of all action and activity. Thought becomes a certain manifestation or expression of existence, but existence is of itself, foundational, autonomous. It is even more interior than our own thoughts, even our own thoughts about our thoughts.

The cogito shows us existence is a principle, but not just any principle. It shows us existence is primarily the self or the individual (or in human nature, the person) and not just any foundation. Matter, for example, is a foundation and a principle, but it is not a principle constituting a self or an individual. The truth of the cogito, in fact, is incompatible with materialism, for it shows us that existence is primarily a self while it is evident that matter is not (nothing common to more than one self could be a self).



  1. Alan Aversa said,

    March 20, 2011 at 4:50 pm

    So the Thomist version would be the converse: Sum, ergo cogito.

    • March 20, 2011 at 5:22 pm

      You’re right that Thomists get the most out of the axiom by stressing the existential note in it, but I think for all that it remains Descartes’s axiom.

      I enjoy your blog, BTW.

      On a side note, 10,000 thank-you’s for finding Mullahy’s thesis. The Scribd version was unreadable, and I desperately wanted to read it.

      • March 20, 2011 at 11:03 pm

        ^I’m glad I decided to read the comments on this one! That work by Mullahy looks very interesting.

      • Alan Aversa said,

        March 21, 2011 at 8:42 am

        Mullahy was a student of De Koninck at Laval.

      • Alan Aversa said,

        March 21, 2011 at 8:55 am

        Also, you might be interested in this, too.

      • March 21, 2011 at 3:20 pm

        Glad I decided to come back and read the comments again. I’ve read a few of those articles actually, but that looks like a very good resource. Thanks a million!

  2. John said,

    March 21, 2011 at 2:36 am


    Another aspect of the Cogito that is often ignored is that Descartes equated thoughts with IDEAS, volitions, judgments etc:

    “5. Of my thoughts some are, as it were, images of things, and to these alone properly belongs the name IDEA; as when I think [ represent to my mind ] a man, a chimera, the sky, an angel or God. Others, again, have certain other forms; as when I will, fear, affirm, or deny, I always, indeed, apprehend something as the object of my thought, but I also embrace in thought something more than the representation of the object; and of this class of thoughts some are called volitions or affections, and others judgments.” (Meditation III).

    If the Cogito does not apply to ideas then it does not apply to judgments, affections etc.

    A Cartesian (or Aristotlean) idea is an entity that has objects arranged in at least two dimensions. A zero dimensional object such as Descartes’ Res Cogitans (his concept of the soul) could indeed be consistent with your claim that “nothing common to more than one self could be a self” but anything with a definite dimensionality, an extension or spread such as an ‘idea’ is potentially accessible to others.

    Descartes invented the Res Cogitans to account for the way that we have a viewing point or “mind’s eye” that appears to contain the content of ideas simultaneously. This invention of a “non-extended place” or Res Cogitans is an early attempt to explain the geometry that is evident in the Cogito: “I have ideas therefore I am”. A modern Descartes would adopt a suitable signature and dimensional number to construct a geometrical form that accounts for the Cogito (See for instance Some notes on Projective Geometry).

%d bloggers like this: