Nothing in the works of the Logical Positivists united them more than Rudolph Carnap's statement that "In the domain of metaphysics, including all philosophy of value and normative theory, logical analysis yields the negative results that the alleged statements in this domain are entirely meaningless." Such statements he meant are not just pointless or false, they are nothing but sequences of words that, however they may appear otherwise, do not make a statement at all.

It is not completely honest to discuss this attitude of Carnap's with Aristotle in mind. The metaphysics that Carnap railed against, like Heidegger's, did not share that strong ground with nature that characterized the philosophies of both Aristotle and the Positivists. In order to avoid the problems of metaphysics Carnap turned to the problem of developing words and sentences with clear and concise meanings.

Concerning the meaning of words, first, Carnap said, we need to determine the syntax of a word in the simplest sentence it is capable of occurring in. He called this an elementary sentence. For example the word stone. The simplest sentence might be "X is a stone." We can call this sentence S. Once this has been determined we must answer the question "What sentence is S deducible from and What sentences are deducible from S?" Once these sentences have been reduced to observation sentences or what are called protocol sentences, that is the meaning of the word. Thus the meaning of a word must be reducible to observation states which can be verified.

Carnap's test of meaningfulness of sentences is as follows. Given any word "a" and an elementary sentence in which "a" occurs, S(a), the necessary and sufficient condition for S(a) being meaningful are given by these formulations.

1. The empirical criteria for "a" are known.

2. It has been stipulated from what protocol sentences S(a) is deducible.

3. The truth conditions for s(a) are fixed.

4. The method of verification for S(a) is known.

A typical metaphysical question, he said, would be "What is the highest principle of the world." In order to determine the meaning of the word "principle" in this sentence we must ask under what conditions the statement X is the principle of Y would be true and under what conditions would it be false. He suggests that the metaphysician would reply that the elementary sentence is true when X arises out of Y or when the being of Y rests on the being of X. However. the concept arising from resting on as the metaphysician is using it has no empirical content, it cannot be verified in experience, and therefore the statement has no meaning.

Another kind of meaningless statement would be those that include meaningful words but still make no sense. For example, the sentence "Caesar is a prime number." has meaningful words and is syntactically correct. However, prime numbers relate only to numbers and not to Caesar. Thus the statement is not false, it is meaningless. Sentences that are not meaningful Carnap called pseudo-statements.

Meaningful statements in philosophy must be both logically and grammatically correct. Such statements cannot be derived from metaphysical concepts. This is particularly important when we come to metaphysical statements that refer to infinite being or infinite non-being. Carnap attacked Heidegger's statements on the role of nothing. These, he claimed, cannot be stated in a logically correct sequence. Metaphysical statements, according to Carnap, are different even than fairy tales. Fairy tales are meaningful but false. Metaphysical statements are nothing but meaningless sequences of words.

The majority of logical mistakes that are committed when pseudo-statements are made are derived from the improper use of the verb to be. An example of the proper use would be, "I am hungry." When the verb is used to import existence then it is being used improperly. An existential statement in logic does not have the form A exists. What it does say is that there exists something of such and such a kind. In a logically correct language constructions that imply existence in this way would not be possible.

When a predicative word is used in a non-predicative meaning this is a problem of type confusion. An example would be the same given before, "Caesar is a prime number." Meaningful statements are divided into the following kinds; Statements that are true solely by virtue of their form (tautologies). The formulae of logic and mathematics are this kind. Kant's analytic statements are this kind. They are not factual. they say nothing about the world. Negatives of the statements above (Contradictions), are self-contradictory and thus false. Empirical statements are the statements of science. They are either true or false determined by their protocol sentences. Any statement that does not fall into one of these two categories is automatically meaningless. a pseudo-statement.

Carnap's "The Old and the New Logic" appeared in the first issue of "Erkenntnis," the short-lived journal of the Logical Positivists, and showed the full pretensions of the young logical Positivists and the kind of energy that set their movement rolling. He pronounced at the outset that "Logic is no longer one philosophical discipline among others. But we are able to say outright: Logic is the method of philosophizing."

The stimulus for the development of this new logic, he said, lay in the need for a critical re-examination of the foundations of mathematics. This became even more important as the existence of logical contradictions became apparent. These required a fundamental reconstruction of logic because Logic is fundamentally tautological. No fact can ever be inferred from another. The conclusion always says the same as the premises only in a different linguistic form. The purpose of philosophy is to decontaminate science. To pursue philosophy is to clarify the concepts and sentences of science by logical analysis through this new logic.

The concept of mind has always had a secondary place in philosophy. Many philosophers refer to it as though there was no equivocation in the term. Aristotle had a sophisticated theory of mind. as did Locke. Hume, on the other hand seemed to treat it like a passive organ making the active part the understanding. However, Carnap and the Positivists saw mind as a metaphysical concept because one could not derive an observation sentence that directly confronted its existence. Thus for Carnap and for many other Positivists alternative explanations had to be developed for what others attributed to mind.

Carnap's purpose in "Psychology in Physical Language" was to show that every sentence of psychology may be formulated in physical language. It is in this article where we will pick up the thread of physicalism in the thought of the logical Positivists. In this article he described two different modes of speech. The material mode which refers to occasions when we speak about material objects, and the formal mode which we use when we speak about the construction of a word or sentence. Note that this is a different distinction from what we have been discussing till now. Thus in Carnap's earlier article as well as with Hahn and others the two modes of speech were speaking about objects and how we speak about objects. The second in this case is not strictly a matter of the form of words and sentences alone, it includes the application of logic and mathematics.

The basis for Carnap's physicalism is his concept of a physical language. Underlying any possible physical language system, Carnap said, are two kinds of languages, The protocol language, the language in which sentences in the immediate mode of speech are developed which express information about the given. And the system language, the language in which the system of science is expressed. A person can verify a sentence in his system language by deducing from sentences in his protocol language and comparing them with his protocol. Now, if a sentence permits no such deductions then it has no meaningful content at all. In the case of psychology, Carnap stated that all of the sentences in psychology can be expressed in a physical language so that if the physical language were chosen as the system language then the protocol languages of psychology would become a subset of the physical language as a result all science would become physics. This statement may be hard to take, but it was his way of saying that psychological statements, both those of everyday life and of scientific psychology, say something about the physical state of the person in question. Later, he put it this way. "It says that psychological statements, both those of everyday life and of scientific psychology, say something about the physical state of the person in question."