Among Descartes’s letters is one in which he discusses the folk notion of truth. He doesn’t use the term “folk;” rather, he uses the term “natural light,” which is similar to how we use the term “folk.” Below the fold I reproduce the important parts of the letter. Then I go on to discuss Descartes’s ambivalence toward the folk intuitions of truth. Thanks to Lex Newman (the philosophy professor and not the poet) for alerting me to the letter.
In a letter to Mersenne on 16 October 1639, Descartes writes [emphasis mine]:
[Lord Herbert of Cherbury's On Truth (1639)] examines what truth is; for my part, I have never had any doubts about truth, because it seems a notion so trascendentally clear that nobody can be ignorant of it. There are many ways of examining a balance before using it, but there is no way to learn what truth is, if one does not know it by nature. What reason would we have for accepting anything which could teach us the nature of truth if we did not know that it was true, that is to say, if we did not know truth? Of course it is possible to explain the meaning of the word to someone who does not know the language, and tell him that the word ‘truth’, in the strict sense, denotes conformity of thought with its object, but that when it is attributed to things outside thought, it means only that they can be the objects of true thoughts, either ours or God’s. But no logical definition can be given which will help anyone to discover its nature. I think the same of many other things which are very simple and are known naturally, such as shape, size, motion, place, time, and so on: if you try to define these things you only obscure them and cause confusion…
The author takes universal consent as the criterion of his truths; whereas I have no criterion for mine except the natural light. The two criteria agree in part: for since all men have the same natural light, it seems that they should have the same notions; but there is also a great difference between them, because hardly anyone makes good use of that light, so that many people – perhaps all those we know – may share the same mistaken opinion. (CSMK 597/598, p. 139)
According to Descartes, truth is something understood naturally. A sentence is true or false when a proposition conforms with the object or state-of-affairs it represents in language. For truth “denotes conformity of thought with its object.” Descartes asserts that we are all aware of what the truth is without having any “logical definition” which “can be given” that “will help anyone to discover its nature.” Either we have an understanding of it or we don’t. If we have an understanding of it, according to Descartes, then the truth of a proposition is its correspondence with reality. If we don’t have an understanding of it, there’s no way we can become aware of it.
Descartes doesn’t fully endorse the reliability of folk intuitions about truth. Notice at the end of the second paragraph he writes: “many people… may share the same mistaken opinion.” In other words, the correct understanding of truth may escape ordinary people’s intuitions, and whatever intuitions we may have gleaned from people may fail to apply because they have not thought about the concept adequately.
Thanks for the explanation. I met the phrase “the natural light” several time in a reading, and got it wrong!
Thank you for the confirmation of Descartes’ expression “natural light.” I am in the process of reading his Meditations for the first time in my Intro to Philosophy course. I sensed he intended a very specific idea when he used this expression and it seems I had intuited it properly after all but I particularly like his idea of the ‘folk notion’ of truth. It was also a treat to read from one of his letters.