Perhaps there is no more striking and unmistakable example of how language and issues of meaning can be wielded on philosophical problems than that of logical positivism. A. J. Ayer (1910–89), in his influential book Language, Truth, and Logic, applied the scalpel of positivism, also called logical empiricism, to issues in ethics, theology, and metaphysics.

The Verification Principle

A. J. Ayer applied a principle called “the verification principle” to statements to see if they were meaningful statements. “To test whether a sentence expresses a genuine empirical hypothesis, I adopt a modified verification principle,” Ayer wrote. “I require of an empirical hypothesis not that it should be conclusively verifiable, but that some possible sense experience should be relevant to the determination of its truth or falsehood. If a putative proposition fails to satisfy this principle, and is not a tautology, then I hold that it is metaphysical and that it is neither true nor false but literally senseless.”

The positivists were not trying to decide whether some statement was true or false. They thought that was the job of science. Philosophy's task was to decide what it means to say that a statement has meaning. A meaningful statement is one that provides information about the world. Ayer's verifiability principle can be illustrated by seeing what he would say about the following statements:

• The cat is on the mat.

• The stock market crashed in October 1931.

• The Chicago Cubs last won the World Series in 1908.

• Michael Jordan owns the highest p.p.g. of all-time (30.1).

• My soul will go to heaven or hell after stopping off in purgatory.

• Krishna is an avatar of Vishnu.

If you are sitting in a room in which there is a cat on the mat, then the first statement is true. Even if there was no cat on the mat, the statement is not meaningless, only false. For at least some “possible sense experience,” in Ayer's words, that would make it true. Statement 2 is false (the market crashed in 1929), but it too is not meaningless. Statements 3 and 4 are true, since they satisfy the empirical demands of the verification principle. But statements 5 and 6 are the kinds that are exposed by Ayer's verification principle. They mention entities like “soul,” “heaven,” “purgatory,” “Krishna,” and “Vishnu.” These entities are metaphysical and cannot be sensed. Thus, the statements are not true or false but “nonsense” — in a very literal way. In fact, you cannot even imagine the kinds of experiences that would verify such entities.

Theological and Moral Statements

A. J. Ayer quotes F. H. Bradley as saying, “The absolute enters into, but is itself incapable of evolution and progress.” But such theological statements cannot be verified or proven false. Similarly, statements such as “All reality is material” or “All reality is immaterial” are beyond the bounds of experience and therefore are neither true nor false, but are pseudo-propositions.

British philosopher Antony Flew makes a point similar to Ayer's about other theological statements. Flew claims that the statement “God loves his children as a father loves his son” is not really falsifiable. In fact, religious people will maintain there is a loving God even when their lives are filled with suffering. Ayer suggests then that such grandiose theological claims are not falsifiable and so are really meaningless.

It is not just the statements themselves but the denial of such statements that are meaningless. So the atheist's assertion that “There is no God” is just as unverifiable and meaningless as the positive claim that there is. At best, metaphysical and theological statements express our feelings about the world.

Even moral statements such as “Abortion is wrong” are senseless, since “wrongness,” unlike “redness,” cannot be sensed. In sum, statements containing value terms, as well as theological and metaphysical terms, make about as much sense as “Turquoise water is virtuous” or “Prufroths blick schoochingly.”

According to positivists, when someone says “You acted wrongly in stealing that money” this does not make a verifiable factual claim about stealing. Instead, when a person morally condemns an act of stealing, what they are actually doing is stating a fact plus expressing an emotion or attitude toward it such as “You stole the money! — Ugh, Boo, Hiss!” This thought was developed further in the “emotivist” philosophy of Charles Stevenson.

According to Ayer, statements in which value terms likes good, evil, right, and just appear are not empirical statements, for they do not describe the world. As such, value statements — like theological and metaphysical statements — are nonsensical.

Positivism and the Legacy of David Hume

You may recall from the chapter on empiricism David Hume's thoughts that you should pick up any volume of divinity or school metaphysics and ask, “Does it contain any abstract reasoning concerning quantity or number? No. Does it contain any experimental reasoning concerning matters of fact and existence? No. Commit it to the flames: for it can contain nothing but sophistry and illusion.”

Much Like Hume, the logical positivists believed all genuine knowledge falls within the two realms of science:

• The formal sciences of logic and mathematics

• The empirical sciences

The first kind of knowledge is expressed in what are called analytic propositions. The truth or falsity of these sorts of statements is based on the logical form of language or on the definition of words. Thus “2 + 2 = 4” and “all bachelors are unmarried” are examples of true analytic statements. Wittgenstein called all such statements tautologies.

False analytic statements, such as “A square has three sides,” or “3 × 3 = 8,” are identified by the fact that they contain a contradiction. Since tautologies are always true and contradictions are always false, no matter what is the case, analytic statements do not give you any factual knowledge about the way the world is.

The second class of statements consists of empirical statements. Unlike analytic statements, both true and false empirical statements do make claims about the world. Since analytic and empirical statements are the only sorts of meaningful statements there are, any proposition that does not fall into either category is not simply false, nor is it merely unknowable, it is meaningless.

Plato's metaphysical assertion that “Forms exist in a world of ideas” cannot be verified. So Ayer would agree with Hume that all pages on which such metaphysical propositions are written should be cast into the flames.