The criterion which we use to test the genuineness of apparent statements of fact is the criterion of verifiability. We say that a sentence is factually significant to any given person, if, and only if, he knows how to verify the proposition which it purports to express—that is, if he knows what observations would lead him, under certain conditions, to accept the proposition as being true, or reject it as being false. If, on the other hand, the putative proposition is of such a character that the assumption of its truth, or falsehood, is consistent with any assumption whatsoever concerning the nature of his future experience, then, as far as he is concerned, it is, if not a tautology, a mere pseudo-proposition.
The sentence expressing it may be emotionally significant to him; but it is not literally significant. And with regard to questions the procedure is the same. We inquire in every case what observations would lead us to answer the question, one way or the other; and, if none can be discovered, we must conclude that the sentence under consideration does not, as far as we are concerned, express a genuine question, however strongly its grammatical appearance may suggest that it does. As the adoption of this procedure is an essential factor in the argument of this book, it needs to be examined in detail. In the first place, it is necessary to draw a distinction between practical verifiability, and verifiability in principle. Plainly we all understand, in many cases believe, propositions which we have not in fact taken steps to verify. Many of these are propositions which we could verify if we took enough trouble. But there remain a number of significant propositions, concerning matters of fact, which we could not verify even if we chose; simply because we lack the practical means of placing ourselves in the situation where the relevant observations could be made.
A simple and familiar example of such a proposition is the proposition that there are mountains on the farther side of the moon. No rocket has yet been invented which would enable me to go and look at the farther side of the moon, so that I am unable to decide the matter by actual observation. But I do know what observations would decide it for me, if, as is theoretically conceivable, I were once in a position to make them. And therefore I say that the proposition is verifiable in principle, if not in practice, and is accordingly significant. On the other hand, such a metaphysical pseudo-proposition as “the Absolute enters into, but is itself incapable of, evolution and progress,” [F.H. Bradley, Appearance and Reality] is not even in principle verifiable. For one cannot conceive of an observation which would enable one to determine whether the Absolute did, or did not, enter into evolution and progress. Of course it is possible that the author of such a remark is using English words in a way in which they are not commonly used by English-speaking people, and that he does, in fact, intend to assert something which could be empirically verified. But until he makes us understand how the proposition that he wishes to express would be verified, he fails to communicate anything to us. And if he admits, as I think the author of the remark in question would have admitted, that his words were not intended to express either a tautology or a proposition which was capable, at least in principle, of being verified, then it follows that he has made an utterance which has no literal significance even for himself. […]
It should now be clear that the only information which we can legitimately derive from the study of our aesthetic and moral experiences is information about our own mental and physical make-up. We take note of these experiences as providing data for our psychological and sociological generalisations. And this is the only way in which they serve to increase our knowledge. It follows that any attempt to make our use of ethical and aesthetic concepts the basis of a metaphysical theory concerning the existence of a world of values, as distinct from the world of facts, involves a false analysis of these concepts. Our own analysis has shown that the phenomena of moral experience cannot fairly be used to support any rationalist or metaphysical doctrine whatsoever. In particular, they cannot, as Kant hoped, be used to establish the existence of a transcendent god.
This mention of God brings us to the question of the possibility of religious knowledge. We shall see that this possibility has already been ruled out by our treatment of metaphysics. But, as this is a point of considerable interest, we may be permitted to discuss it at some length. It is now generally admitted, at any rate by philosophers, that the existence of a being having the attributes which define the god of any non-animistic religion cannot be demonstratively proved. To see that this is so, we have only to ask ourselves what are the premises from which the existence of such a god could be deduced. If the conclusion that a god exists is to be demonstratively certain, then these premises must be certain; for, as the conclusion of a deductive argument is already contained in the premises, any uncertainty there may be about the truth of the premises is necessarily shared by it. But we know that no empirical proposition can ever be anything more than probable. It is only a priori propositions that are logically certain. But we cannot deduce the existence of a god from an a priori proposition. For we know that the reason why a priori propositions are certain is that they are tautologies. And from a set of tautologies nothing but a further tautology can be validly deduced. It follows that there is no possibility of demonstrating the existence of a god.
What is not so generally recognised is that there can be no way of proving that the existence of a god, such as the God of Chrisianity, is even probable. Yet this also is easily shown. For if the existence of such a god were probable, then the proposition that he existed would be an empirical hypothesis. And in that case it would be possible to deduce from it, and other empirical hypotheses, certain experiential propositions which were not deducible from those other hypotheses alone. But in fact this is not possible. It is sometimes claimed, indeed, that the existence of a certain sort of regularity in nature constitutes sufficient evidence for the existence of a god. But if the sentence “God exists” entails to more than that certain types of phenomena occur in certain sequences, then to assert the existence of a god will be simply equivalent to asserting that there is the requisite regularity in nature; and no religious man would admit that this was all he intended to assert in asserting the existence of a god. He would say that in talking about God, he was talking about a transcendent being who might be known through certain empirical manifestations, but certainly could not be defined in terms of those manifestations. But in that case the term “god” is a metaphysical term. And if “god” is a metaphysical term, then it cannot be even probable that a god exists. For to say that “God exists” is to make a metaphysical utterance which cannot be either true or false. And by the same criterion, no sentence which purports to describe the nature of a transcendent god can possess any literal significance.
It is important not to confuse this view of religious assertions with the view that is adopted by atheists, or agnostics. For it is characteristic of an agnostic to hold that the existence of a god is a possibility in which there is no good reason either to believe or disbelieve; and it is characteristic of an atheist to hold that it is at least probable that no god exists. And our view that all utterances about the nature of God are nonsensical, so far from being identical with, or even lending any support to, either of these familiar contentions, is actually incompatible with them. For if the assertion that there is a god is nonsensical, then the atheist’s assertion is that there is no god is equally nonsensical, since it is only a significant proposition that can be significantly contradicted. As for the agnostic, although he refrains from saying either that there is or that there is not a god, he does not deny that the question whether a transcendent god exists is a genuine question. He does not deny that the two sentences “There is a transcendent god” and “There is no transcendent god” express propositions one of which is actually true and the other false. All he says is that we have no means of telling which of them is true, and therefore ought not to commit ourselves to either. But we have seen that the sentences in question do not express propositions at all. And this means that agnosticism also is ruled out.
Thus we offer the theist the same comfort as we gave to the moralist. His assertions cannot possibly be valid, but they cannot be invalid either. As he says nothing at all about the world, he cannot justly be accused of saying anything false, or anything for which he has insufficient grounds. It is only when the theist claims that in asserting the existence of a transcendent god he is expressing a genuine proposition that we are entitled to disagree with him.
It is to be remarked that in cases where deities are identified with natural objects, assertions concerning them may be allowed to be significant. If, for example, a man tells me that the occurrence of thunder is alone both necessary and sufficient to establish the truth of the proposition that Jehovah is angry, I may conclude that, in his usage of words, the sentence “Jehovah is angry” is equivalent to “It is thundering.” But in sophisticated religions, though they may be to some extent based on men’s awe of natural process which they cannot sufficiently understand, the “person” who is supposed to control the empirical world is not himself located in it; he is held to be superior to the empirical world, and so outside it; and he is endowed with super-empirical attributes. But the notion of a person whose essential attributes are non-empirical is not an intelligible notion at all. We may have a word which is used, as if it named this “person,” but, unless the sentences in which it occurs express propositions which are empirically verifiable, it cannot be said to symbolize anything. And this is the case with regard to the word “god,” in the usage in which it is intended to refer to a transcendent object. The mere existence of the noun is enough to foster the illusion that there is a real, or at any rate a possible entity corresponding to it. It is only when we enquire what God’s attributes are that we discover that “God,” in this usage, is not a genuine name.
It is common to find belief in a transcendent god conjoined with belief in an after-life. But, in the form which it usually takes, the content of this belief is not a genuine hypothesis. To say that men do not ever die, or that the state of death is merely a state of prolonged insensibility, is indeed to express a significant proposition, though all the available evidence goes to show that it is false. But to say that there is something imperceptible inside a man, which is his soul or his real self, and that it goes on living after he is dead, is to make a metaphysical assertion which has no more factual content than the assertion that there is a transcends god.
It is worth mentioning that, according to the account which we have given of religious assertions, there is no logical ground for antagonism between religion and natural science. As far as the question of truth or falsehood is concerned, there is no opposition, between the natural scientist and the theist who believes in a transcendent god. For since the religious utterances of the theist are not genuine propositions at all, they cannot stand in any logical relation to the propositions of science. Such antagonism as there is between religion and science appears to consist in the fact that science takes away one of the motives which make men religious. For it is acknowledged that one of the ultimate sources of religious feeling lies in the inability of men to determine their own destiny; and science tends to destroy the feeling of awe with which men regard an alien world, by making them believe that they can understand and anticipate the course of natural phenomena, and even to some extent control it. The fact that it has recently become fashionable for physicists themselves to be sympathetic towards religion is a point in favour of this hypothesis. For this sympathy towards religion marks the physicists’ own lack of confidence in the validity of their hypotheses, which is a reaction on their part from the anti-religious dogmatism of nineteenth-century scientists, and a natural outcome of the crisis through which physics has just passed.
It is not within the scope of this enquiry to enter more deeply into the causes of religious feeling, or to discuss the probability of the continuance of religious belief. We are concerned only to answer those questions which arise out of our discussion of the possibility of religious knowledge. The point which we wish to establish is that there cannot be any transcendent truths of religion. For the sentences which the theist uses to express such “truths” are not literally significant.
A. J. Ayer, Language Truth and Logic [New York: Dover Publications. 1946] pp. 35-37, 114-18.