Truth, for so many thinkers throughout history, has been seen as existing independent of human minds. But it seems far more sensible to embrace an anthropological account of truth which Robert Adams nicely describes as the view “that the truths of logic and mathematics are true in virtue of some feature of human thought, which might be ideas in our heads, our intentions regarding our use of language, or proofs we have actually constructed.” (see his book Leibniz: Determinist, Theist, Idealist, p. 182) But this view, while initially plausible, seems to have the following undesirable and counter-intuitive implications that, once understood, may make a commitment to an inhuman ground of truth more attractive: (1) there are no propositions whose truth or falsity we have not yet uncovered or will never uncover; (2) there are true propositions that have no contradictories which threatens the foundations of logic; (3) human communication about the same concepts and propositions would seem impossible; (4) truth, rather than our estimations of the truth, would change; (5) there would be no necessary truths, that is, truths that are true in all possible worlds; and (6) the impressive applicability of necessary truths to the physical world becomes unacceptably mysterious. Let me take each in turn.
(1) and (2) can be approached by considering a thought-experiment presented by Bradley and Swartz. Suppose someone is walking alone in the woods and encounters a birch tree which he correctly believes is a birch. Thus, according to the theory that propositions are human creations, we would maintain that the person has a true proposition in his mind or brain, a proposition that doesn’t exist independently of the man and which came into existence with his encounter and consideration of the tree. Now, suppose further that the birch subsequently burns down in a forest fire and no one ever entertains the false proposition that the tree the man encountered was not a birch. This would mean, as Bradley and Swartz point out, “we would have to give up the claim that to every truth there corresponds a non-empty class of falsehoods each of which is a contradictory of that truth. Under this proposal, some truths and some falsehoods would be without contradictories. Not only would this make shambles of logic; it is thoroughly counterintuitive as well. We have a strong disposition to insist that even if no one were to believe of the birch tree that it is not a birch, then were anyone to believe it, what he would believe is false” (see their book Possible Worlds, p. 70). So by agreeing that propositions are not human constructions we can, first and foremost, account for our intuitions that there are propositions independent of us whose truth value we don’t know yet or will never know. But we can also save logic since to even begin truth functional logic we need to maintain that every proposition has two possible values: true and false. But if propositions are things created by humans then, as the thought experiment shows, we are bound to have propositions with only one possible truth value.
(3), that human communication about the same concepts and propositions would be impossible, seems to follow if we only share information about our own subjective versions of concepts and propositions that reside in our particular, changing, and unique minds. But if propositions are independent of human minds then perhaps we can think and talk about the same concepts and propositions (for example the Pythagorean Theorem).
(4) In his dialogue On Free Choice of the Will (Macmillan, 1964) St. Augustine wrote: “If truth were equal to our minds, it would be subject to change. Our minds sometimes see more and sometimes less, and because of this we acknowledge that they are mutable. Truth, remaining in itself, does not gain anything when we see it, or lose anything when we do not see it” (p. 67). If so-called true propositions reside in our changing minds then truth would change which is absurd. To be sure, our estimations of the truth change. But not the truth itself.
(5) If all truth is a function of human beings then, since humans are contingent beings that at one time didn’t exist, we would have to accept that truth is as contingent as we are. Perhaps we could embrace some forms of relative necessity in which certain things necessarily follow once a set of contingent limitations is established. For example: (a) It is not physically possible to go faster than the speed of light given the laws of nature as we currently understand them. But these laws, we can easily imagine, could be different in a different possible world or indeed our own. (b) It is not biologically possible for me, given my genetic make up, to naturally sprout some wings and fly. But we can easily imagine a different genetic makeup for me in a different possible world. (c) It is not possible for someone living in New York to legally have many wives given the laws of the state. But we can easily imagine the laws being changed. In each of these cases there is a form of necessity in place which, upon consideration, is revealed to be relative or contingent: relative to certain conditions such as laws of nature, biology, and the state. But it seems unacceptable to reduce necessity to relative necessity since, as Marsilio Ficino points out in volume four of his Platonic Theology (Harvard: 2001),
“Every intellect is aware of a necessary consequence in things which are contingent or non-existence. For instance, it is a necessary consequence that, if Plato runs, he moves, even though Plato, his running, and his moving are themselves contingents. It is necessary too that when Plato argued Plato was talking, although neither Plato nor his argument nor his enunciation of it are occurring in the present. The unchanging necessity of such consequences is not based on the things in time, which are totally non-existent or contingent; nor does it rest solely on the thoughts of the soul, or it would not be true necessity but a mental fiction, or rather it would not be immutable since our thinking changes.” (p. 95).
Indeed, most of us want to embrace forms of necessity that are not contingent. And understanding these forms of necessity may allow us to define relative necessity in the first place. Joseph Melia comments on both these points in his book Modality: “There are indeed many forms of necessity. But many can be defined in terms of what is (absolutely) compatible with a certain set of facts, which we have arbitrarily decided to keep fixed. Throughout, a particular kind of necessity – absolute necessity – is needed to define these various relative modalities. Moreover, the mere notion of relative modality is not enough to capture a distinction we want to capture: a distinction in kind between the laws of logic and the laws of biology; a distinction in kind between the laws of mathematics and the laws of physics – a distinction between what is absolutely necessary and what is absolutely contingent” (pp. 17-18). But if we accept the anthropological account of truth then we will lack absolute necessity and, perhaps, the ability to define forms of relative necessity as well.
(6), or the claim that the impressive applicability of necessary truths to the physical world becomes unacceptably mysterious, is nicely presented in the form of a question by Bradley and Swartz: “[I]f these necessary truths are merely the result of arbitrary human conventions for the use of mathematical symbols, all this becomes a seeming miracle. Why should the world conform so felicitously to the consequences of our linguistic stipulations?” They argue that it is precisely by embracing necessary truths as propositions which are true in all possible worlds, including worlds without humans, that we can provide an adequate explanation of their application in engineering, aeronautics, and so on: “Necessary truths, such as those of mathematics, apply to the world because they are true in all possible worlds; and since the actual world is a possible world it follows that they are true in (i.e., apply to) the actual world” (Possible Worlds, p. 61).
If this cumulative case against the anthropological view of truth succeeds then truth wouldn’t be a human construction. Rather, when we think true propositions we would be contacting entities independent of ourselves. But what would these entities be? Could they be, as Augustine argued, ideas in God’s mind? Could they be propositions in multiple non-human minds? Might they be abstract entities that exist outside of space and time independent of all minds as some Platonists believe? Or could true propositions be facts or states of affairs as Bertrand Russell once maintained? Are there some other plausible options? What are they?