Despite the vigorous and in some ways salutary challenge it offered, the programme of the positivists for the ‘elimination of metaphysics’ had ground to a halt by the 1960s. There turned out to be serious problems in formulating the verification principle in a way which was stringent enough to exclude traditional metaphysics, yet liberal enough to accommodate the complex theoretical statements of natural science.
There have been many opponents of metaphysics from the Greek sceptics to the empiricists of the nineteenth century. Criticisms of very diverse kinds have been set forth. Many have declared that the doctrine of metaphysics is false, since it contradicts our empirical knowledge. Others have believed it to be uncertain, on the ground that its problems transcend the limits of human knowledge. Many anti-metaphysicians have declared that occupation with metaphysical questions is sterile. Whether or not these questions can be answered, it is at any rate unnecessary to worry about them; let us devote ourselves entirely to the practical tasks which confront active men every day of their lives!
The development of modern logic has made it possible to give a new and sharper answer to the question of the validity and justification of metaphysics. The researches of applied logic or the theory of knowledge, which aim at clarifying the cognitive content of scientific statements and thereby the meanings of the terms that occur in the statements, by means of logical analysis, lead to a positive and to a negative result. The positive result is worked out in the domain of empirical science; the various concepts of the various branches of science are clarified; their formal, logical and epistemological connections are made explicit. In the domain of metaphysics, including all philosophy of value and normative theory, logical analysis yields the negative result that the alleged statements in this domain are entirely meaningless. Therewith a radical elimination of metaphysics is attained, which was not yet possible from the earlier anti-metaphysical standpoints …
In saying that the so-called statements of metaphysics are meaningless, we intend this word in its strictest sense. In a loose sense of the word a statement or a question is at times called meaningless if it is entirely sterile to assert or ask it. We might say this for instance about the question ‘what is the average weight of those inhabitants of Vienna whose telephone number ends with “3”?’ or about a statement which is quite obviously false like ‘in 1910 Vienna had 6 inhabitants’ or about a statement which is not just empirically, but logically false, a contradictory statement such as ‘persons A and B are each a year older than the other’. Such sentences are really meaningful, though they are pointless or false; for it is only meaningful sentences that are even divisible into (theoretically) fruitful and sterile, true and false. In the strict sense, however, a sequence of words is meaningless if it does not, within a specified language, constitute a statement. It may happen that such a sequence of words looks like a statement at first glance; in that case we call it a pseudo-statement. Our thesis, now, is that logical analysis reveals the alleged statements of metaphysics to be pseudo-statements…
A word which (within a definite language) has a meaning, is usually also said to designate a concept; if it only seems to have a meaning while it really does not, we speak of a ‘pseudo-concept’. How is the origin of a pseudo-concept to be explained? Has not every word been introduced into the language for no other purpose than to express something or other, so that it had a definite meaning from the very beginning of its use? How, then, can a traditional language contain meaningless words? To be sure, originally every word (excepting rare cases which we shall illustrate later) had a meaning. In the course of historical development a word frequently changes its meaning. And it also happens at times that a word loses its old sense without acquiring a new one. It is thus that a pseudo-concept arises.
What, now, is the meaning of a word? What stipulations concerning a word must be made in order for it to be significant? (It does not matter for our investigation whether these stipulations are explicitly laid down, as in the case of some words and symbols of modern science, or whether they have been tacitly agreed upon, as is the case for most words of traditional language.) First, the syntax of the word must be fixed, i.e. the mode of its occurrence in the simplest sentence form in which it is capable of occurring; we call this sentence form its elementary sentence. The elementary sentence form for the word ‘stone’ e.g. is ‘x is a stone’; in sentences of this form some designation from the category of things occupies the place of ‘x’, e.g. ‘this diamond’, ‘this apple’. Secondly, for an elementary sentence S containing the word, an answer must be given to the following question, which can be formulated in various ways:
(1) What sentences is S deducible from, and what sentences are deducible from S?
(2) Under what conditions is S supposed to be true, and under what conditions false?
(3) How is S to be verified?
(4) What is the meaning of S?
… In the case of many words, specifically in the case of the overwhelming majority of scientific words, it is possible to specify their meaning by reduction to other words … e.g. “‘arthropods” are animals with segmented bodies and jointed legs’. Thereby the above-mentioned question for the elementary sentence form of the word “arthropod”, that is for the sentence form “the thing x is an arthropod”, is answered: it has been stipulated that a sentence of this form is deducible from premises of the form “x is an animal”, “x has a segmented body”, “x has jointed legs”, and that conversely each of these sentences is deducible from the former sentence. By means of these stipulations about deducibility (in other words: about the truth-condition, about the method of verification, about the meaning) of the elementary sentence about “arthropod”, the meaning of the word “arthropod” is fixed. In this way every word of the language is reduced to other words and finally to the words which occur in the so-called “observation sentences” or “protocol sentences”. It is through this reduction that the word acquires its meaning.
For our purposes we may ignore entirely the question concerning the content and form of the primary sentences (protocol sentences) which has not yet been definitely settled. In the theory of knowledge it is customary to say that the primary sentences refer to ‘the given’; but there is no unanimity on the question what it is that is given. At times the position is taken that sentences about the given speak of the simplest qualities of sense and feeling (e.g. ‘warm’, ‘blue’, ‘joy’ and so forth); others incline to the view that basic sentences refer to total experiences and similarities between them; a still different view has it that even the basic sentences speak of things. Regardless of this diversity of opinion it is certain that a sequence of words has a meaning only if its relations of deducibility to the protocol sentences are fixed, whatever the characteristics of the protocol sentences may be; and similarly, that a word is significant only if the sentences in which it may occur are reducible to protocol sentences.
Since the meaning of a word is determined by its criterion of application (in other words by the relations of deducibility entered into by its elementary sentence-form, by its truth-conditions, by the method of its verification), the stipulation of the criterion takes away one’s freedom to decide what one wishes to ‘mean’ by the word. If the word is to receive an exact meaning, nothing less than the criterion of application must be given; but one cannot, on the other hand, give more than the criterion of application, for the latter is a sufficient determination of meaning. The meaning is implicitly contained in the criterion; all that remains to be done is to make the meaning explicit.
Let us suppose, by way of illustration, that someone invented the new word ‘teavy’ and maintained that there are things which are teavy and things which are not teavy. In order to learn the meaning of this word, we ask him about its criterion of application: how is one to ascertain in a concrete case whether a given thing is teavy or not? Let us suppose to begin with that we get no answer from him: there are no empirical signs of teavyness, he