And that is fine for those who have decided to follow an aesthetic religion. But John of the Cross would have told us that it was only his mystical experience of the Absolute that assured him of the only possible truth. This has led many men of faith to the conviction that those philosophers who reject the possibility of knowing the Absolute are automatically rejecting every criterion of truth, or by rejecting such a thing as an absolute criterion of truth, they are rejecting the possibility of experiencing the Absolute. But it is one thing to say that a philosophy rejects the possibility of knowing the Absolute, and another thing to say that it rejects every criterion of truth—even that relating to the contingent world. Are truth and experience of the Absolute then so inseparable?
Confidence that something is true is fundamentally important for the survival of human beings. If we were unable to consider that what others tell us is either true or false, society would not be possible. We wouldn’t even be able to exclude the possibility that a box with ASPIRIN written on it didn’t in fact contain strychnine.
A specular theory of truth is that it is adaequatio rei et intellectus, as if our mind were a mirror that, provided it works properly and is not distorted or misted, must truly reflect things as they are. It is a theory supported, for example, by Thomas Aquinas, but also by Lenin in Materialism and Empirio-criticism (1909), and since Aquinas could not have been a Leninist, it ought to follow that Lenin was a neo-Thomist—without, of course, realizing it. In reality, other than in states of ecstasy, we are obliged to say what our mind reflects. Nevertheless, we define as true (or false) not the things themselves but the assertions we make about how things are. Alfred Tarski’s famous definition says that the statement “Snow is white” is true if, and only if, snow is white. Let us leave aside for the moment the whiteness of snow, which is more and more open to dispute, and consider another example: the statement “It is raining” (set between quotation marks) is true only if outside it is raining (without quotation marks).
The first part of the definition (between quotation marks) is a verbal statement and represents nothing other than itself, but the second part should express how things in fact are. Nevertheless, something that ought to be a state of things is expressed once again in words. To avoid this linguistic mediation we ought to say that “It is raining” (between quotation marks) is true if there is that thing there (and, without saying anything, we point to the rain that is falling). But although this way of indicating the evidence of the senses can be used with rain, it would be more difficult to do the same with the statement “Earth revolves around the sun” (since, if anything, the senses would tell us quite the opposite).
To establish whether the statement corresponds to a particular set of circumstances, it is necessary to have interpreted the word rain and to have formed a definition of it. It needs to have been established that (a) to talk of rain it is not enough to feel drops of water falling from above (as there could be someone watering flowers on a balcony above), (b) the drops must be of a certain consistency (otherwise we would talk of mist or frost), (c) the sensation must be continuous (otherwise we would say it was trying to rain but had come to nothing), and so forth. Having decided this, we have to pass on to an empirical test, which in the case of rain can be done by anyone (all we have to do is hold out our hand and trust our senses).
But in the case of the statement “Earth revolves around the sun,” the ways for testing it are more complex. What meaning does the word true have for each of the following statements?
I have a stomachache.
Last night I dreamed that Mother Teresa appeared to me.
Tomorrow it will certainly rain.
The world will end in 2536.
There is life after death.
Statements 1 and 2 express a subjective fact, but the stomachache is a clear and irrepressible sensation, whereas when I recall a dream I had last night, I may not be sure the memory is accurate. What is more, the two statements cannot be directly verified by other people. A doctor would, of course, have certain ways of checking whether I actually have gastritis or whether I’m a hypochondriac, but a psychoanalyst would have more difficulty if someone tells him she has seen Mother Teresa in a dream, since she could easily be lying.
Statements 3, 4, and 5 are not directly verifiable. But whether it will rain tomorrow can be verified tomorrow, whereas whether the world will end in 2536 is rather more of a problem (and here we distinguish between the reliability of a weather forecaster and that of a prophet). The difference between statements 4 and 5 is that 4 will become true or false in 2536, whereas 5 will continue to remain empirically undecidable per saecula saeculorum.
Now let’s consider these statements:
6. The sum of the angles of a triangle is 180 degrees.
7. Water boils at 100 degrees Celsius.
8. The apple is an angiosperm.
9. Napoleon died on May 5, 1821.
10. We reach the coast following the path of the sun.
11. Jesus is the Son of God.
12. The correct interpretation of the holy scriptures is decided by the teachings of the church.
13. An embryo is already a human being and has a soul.
Some of these statements are true or false according to the rules we have stipulated: the sum of the angles of a triangle is 180 degrees only in the context of a Euclidean system of postulates; that water boils at a hundred degrees at standard atmospheric pressure, that is, at sea level, is true not only if we accept a law of physics elaborated through inductive generalization, but also on the basis of the definition of degrees centigrade; an apple is an angiosperm only on the basis of certain rules of botanical classification.
Some require us to trust facts ascertained by others before us: we believe it is true that Napoleon died on May 5, 1821, because we accept what the history books tell us, but we must always recognize the possibility that an unpublished document discovered tomorrow in the British naval archives might show that he died on another date. Sometimes for utilitarian reasons we adopt an idea as true that we know to be false: for example, to find our way in the desert, we behave as if it were true that the sun moves from east to west.
As for statements of a religious nature, we shall not say they are undecidable. If the evidence of the Gospels is accepted as historical, the proof of the divinity of Christ would be accepted as such by a Protestant. But this would not be so for the teachings of the Catholic Church. The statement regarding embryos having a soul depends entirely on stipulating the meanings of expressions such as life, human, and soul. Thomas Aquinas, for example (see the essay “No Embryos in Paradise”), claimed that, like animals, they had only a sensitive soul and therefore were not yet human beings equipped with a rational soul, and would not participate in the resurrection of the flesh. Today he would be accused of heresy, but at that very civilized time they made him a saint.
It is therefore a matter of deciding each time which criteria for truth we are using.
It is on the very recognition of various degrees of verifiability or acceptability of a truth that our sense of tolerance is based. I may be obliged, from a scientific and educational point of view, to fail a student who claims that water boils at ninety degrees, like the right angle—as was apparently once suggested in an exam—but even a Christian ought to accept that for some people there is no other god than Allah and Muhammad is his prophet (as we likewise ask Muslims to do for Christians concerning Christian doctrine).