(a) The Meaning of "Metaphysics"
(b) Scientific Positivism
(c) Logical Positivism
(d) Criticism of Positivism
(a) The Meaning of "Metaphysics" — Several times we have raised issues which have been called metaphysical. It is time to form a clearer idea as to the meaning of "metaphysics," and to enquire whether metaphysics is a possible kind of study or only an impossible dream.
The word "metaphysics" is ambiguous. In the widest of all its possible senses it seems to mean the attempt to discover, by whatever method, the most general or comprehensive principles that are true of the experienced universe, or of everything in the experienced universe, or simply of "reality." A more usual and somewhat more restricted sense is the attempt to discover by logical analysis of experience the most general principles that are true of the universe as we experience it. This is what Kant called "immanent metaphysics," in contrast with the still more restricted "transcendent metaphysics." By "transcendent metaphysics" he meant the attempt to discover by reasoning the nature of the reality which was conceived to lie behind the world of our ordinary experience. In the following discussion we shall be considering metaphysical theories of various types, but we must always bear in mind Kant's distinction, and his contention that though "immanent metaphysics" was a possible study, "transcendent metaphysics" was logically impossible. There is no need, of course, to suppose that the distinction between the kinds of metaphysics is always easy to apply.
The starting-point of metaphysics in either sense is the desire to construct a comprehensively true description of reality. But "transcendent metaphysics" proceeds on the assumption that, since the experienced world is incoherent and unintelligible, we must suppose it to be in some sense merely an "appearance" of a hidden "reality." The method by which it is hoped to discover reality is rational analysis of the fundamental concepts or categories in terms of which we think about things. Though our perception of reality, and our thought about reality. are confused and self-contradictory, it is supposed that, if only we think hard enough, penetratingly enough, sincerely enough, about the nature of our experience, we may discover some hidden principles in the light of which the whole confusion will be resolved.
Two kinds of fundamental criticism are brought against metaphysics. One is derived from natural science, the other from the logical limitations of our thinking. We will consider them in turn.
(b) Scientific Positivism — The gradual realisation of the immense size, complexity, and subtlety of the physical universe has made it seem unlikely that man should be able to discover anything about the fundamental nature of reality. Man has existed for a very short time. Is it credible that the upstart intelligence of a minute organism should be capable of understanding the essence of everything? Human intelligence, as we have seen, evolved as a means of mastering practical problems, such as the struggle for food and safety. Was it likely that this humble instrument could accomplish a task that was profoundly alien to it?
This argument was confirmed by the fact that metaphysics seemed never to make any progress. For many centuries the philosophers had been at work, yet what was there to show for it? There was no agreement among them on metaphysical questions. Science, on the other hand, had moved on from strength to strength. Of course there was plenty of disagreement among scientists; but it was disagreement only along the ever-advancing front of scientific conquest. Behind lay a well-established régime which no one would dream of disputing.
Swayed by such arguments Auguste Comte and others formulated the doctrine of Positivism. All metaphysical problems must be foresworn as beyond the range of human intelligence. The only profitable intellectual task was to pursue the scientific exploration of the world.
(c) Logical Positivism — This sceptical disposition has been outdone by the Logical Positivists. According to them, metaphysics is not merely too difficult for the human intellect to tackle profitably; it is logically an impossible task. We have several times had occasion to notice this important argument. It is now time to pass our final judgment on it. Mr. A. J. Ayer, in his Language Truth and Logic, affirms that, since the metaphysician claims to know by intellectual processes facts that could not be known through sense-experience, and since "no statement which refers to a 'reality' transcending the limits of all possible sense-experience can possibly have any literal significance," all metaphysics must necessarily be nonsense. The fruitlessness of trying by means of logical argument to transcend the limits of all possible sense-experience follows, according to the Logical Positivists, from the nature of the significance of language. The metaphysician, we are told, produces sentences which "fail to conform to the conditions under which alone a sentence can be literally significant." A sentence can only be significant, it is said, if it is verifiable. The only way in which to verify a statement of fact (as distinct from a purely logical, and therefore tautological, statement) is by producing the relevant sense-experience. All statements of fact, if they are to have any meaning, must be verifiable at least in principle in sense-experience. Of course it must be admitted that many meaningful statements of fact cannot actually be verified in sense-experience, because we cannot put ourselves in the position to have the relevant sense-experience. Of this type is the statement that there are mountains on the other. side of the moon. This is not a meaningless statement, because at least we know what kind of experience would afford verification of it. On the other hand, in the case of metaphysical statements it is argued that no kind of conceivable sense-experience could possibly, even in theory, afford verification. Therefore all such experiences are meaningless. For instance, the statement that God is an eternal spirit cannot conceivably be verified by any kind of sense-experience, because sense-experience is essentially temporal. It comes into being and then vanishes. Verification of the statement that God is an eternal spirit would have to be given in a sense-experience that was itself eternal. But this is inconceivable to us. Similarly unverifiable and meaningless is the statement that reality, as opposed to mere appearance, is timeless. Other examples are the statements that reality is one substance, or two, or many, or unknowable.
The Logical Positivist's rejection of metaphysics may take another form. According to the theory, logical necessity (as we have already seen) is nothing more than tautology. Logical argument is mere elucidation of the content of a definition. It follows that the attempt to discover an underlying reality simply by deductive reasoning is futile. No doubt the definitions or concepts which metaphysics analyses are in the first instance derived from our experience of reality; and, taken at their face-value, they are approximately true of experienced reality. But we have no guarantee whatever that the analysed or deduced content of them is true also of a reality which we cannot experience.
(d) Criticism of Positivism — What is the real value of these arguments? Let us begin by distinguishing several kinds of "metaphysical" statements. Some metaphysical statements of the "immanent" kind really are theoretically verifiable in sense-experience in precisely the same manner as, for example, the statement that this book was written by a human being. The statement that there is in the universe "a power that makes for righteousness" is theoretically verifiable. If a large number of spectacular miracles were to occur, all of which obviously produced great good in the world, we should reasonably regard this as strong evidence that some superhuman power was interfering with the natural course of events so as to produce good results. Logical Positivists might claim that even such a crop of miracles would not verify the statement about a benevolent power, but merely the statement that such events had occurred. This is surely unsatisfactory. If a savage were to hear intelligible speech issuing from a radio loud-speaker, or from a gramophone, he would be justified in inferring that an intelligent being had determined the order of the sounds, in spite of the fact that he could not possibly conceive how the mi............