What was Logical Positivism and its Verification Principle?


Logical positivism was a philosophical movement that flourished between 1920 and 1960 in several centers across Europe and the United States. The movement’s proponents were all empiricists of a kind (those who believe that knowledge is principally derived from sense experience and observation) and many of them shared interests in thinking about how science and scientific methodology could reshape society.

Ludwig Wittgenstein and the Verification Principle

In the mid-20th century the Vienna Circle, which consisted of a group of thinkers including philosophers and scientists, proposed that only logical truths and statements about the physical world have meaning. This position became known as logical positivism, a philosophy significantly influenced by Ludwig Wittgenstein’s (1889-1951) picture theory of meaning. Although he would later revise and alter his views, Wittgenstein, in his Tractatus Logico-Philosophicus (1922), argued that language enables people to form pictures of reality that they are then able to share with others in order to find a common understanding. This became known as Wittgenstein’s picture theory of language, which would influence thinkers within the Vienna Circle. The theory proved influential because it also argued that only words which refer to empirical objects are meaningful; words like “grass” and “green” are the building blocks of the meaningful statement, whereas statements that cannot be reduced to atomic propositions are nonsense because they fail to describe reality.

The logical positivists agreed and stated that propositions of science are meaningful and make sense, whereas statements of theology, ethics, and aesthetics do not. Logical positivism’s central rule was what became known as the verification principle, according to which a statement only has value and meaning if it is logically true or can be verified by observation. A number of proponents had the goal of exorcising speculation from philosophy so that it could be brought into line with modern science.

A. J. Ayer

The British empiricist philosopher A.J. Ayer (1910-1989) was a major proponent of logical positivism. He penned Language, Truths and Logic (1936) in which he argued that only empirical, tautological, or mathematical statements are meaningful because these include only those things that can be verified by observation, logic, or mathematics, while other statements, such as those of theology (i.e. “God is good”), ethical statements (i.e. “rape is evil”), and aesthetic statements (i.e. “the mountain is beautiful”), do not express meaningful ideas and are therefore meaningless. Ayer stated that “all utterances about the nature of God are nonsensical” and this would even include atheist and agnostic assertions. And for the believer in God, “his assertions cannot be valid, but they cannot be invalid either” (1). Ayer continues,

“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 expresses 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” (2).

For the logical positivists, there are only two types of meaningful statements: logical statements (such as “Red is a colour”, or “A triangle has three sides”) and factual statements (such as “It is snowing outside”, or “The sun is shining”). In contrast to statements of ethics, aesthetics, and theology, these are meaningful because they express logical truths and/or are related to the observable world.

Rudolf Carnap Renounces Metaphysics

Rudolf Carnap (1891-1970), a member of the Vienna Circle and an admirer of Wittgenstein’s picture theory of meaning, was also critical of meaningless speculation which failed to satisfy the verification principle. Carnap believed that philosophers had spent too much time speculating about the nature of reality, which led him to claim that they should restrict themselves to analyzing language, while philosophy itself should be a rigorous, empirical discipline. In a similar light to the views of Bertrand Russell (1872-1970), Carnap believed that confusion is avoidable by using logical analysis which revealed the underlying logic of ordinary language. The philosopher should identify language in the same way physicists have identified fundamental laws of nature lying behind the natural order. Carnap reasoned that the fundamental laws of philosophy are the laws of logic, although he believed there is an important difference between them and the laws of science,

“Logic is not concerned with human behavior in the same sense that physiology, psychology, and social sciences are concerned with it. These sciences formulate laws or universal statements which have as their subject matter human activities as processes in time. Logic, on the contrary, is concerned with relations between factual sentences (or thoughts)” (3).

Similarly to Ayer, Carnap used the verification principle to judge statements and argued that those of a metaphysical kind which cannot be verified by experience (statements such as “God is good” and “the soul survives death”) are strictly meaningless. He called such sentences “pseudo-sentences”,

“According to this view, the sentences of metaphysics are pseudo-sentences which on logical analysis are proved to be either empty phrases or phrases which violate the rules of syntax. Of the so-called philosophical problems, the only questions which have any meaning are those of the logic of science. To share this view is to substitute logical syntax for philosophy” (4).

It is clear then that to Carnap many sentences used in daily language by human beings make no sense and have no meaning, a view informed by the conviction that it was impossible to marshal any evidence in support of metaphysical claims and that metaphysical theories of both the past (i.e. Plato’s theory of forms, Descartes’ cogito, and Hegel’s concept of Geist) and the present should be abandoned. Philosophers should not construct theories about the world because this is the prerogative of science.

Criticisms of Logical Positivism

Despite its legacy, logical positivism is no longer a popular philosophical theory and its rejection of metaphysics has come under scrutiny. Already in 1967 the Australian philosopher John Passmore (1914-2004) stated that “Logical positivism, then, is dead, or as dead as a philosophical movement ever becomes” (5).

Most contemporary philosophers are hesitant to pronounce the death of metaphysics. William Lane Craig explains that “Since the demise of Verificationism in the mid-twentieth century, metaphysics, despite Kant’s strictures, has been booming once again” (5). Logical positivism lost its potency when philosophers agreed that its verification principle would not only render theological statements meaningless but also “a great many scientific statements—along with ethical, aesthetic, and metaphysical statements as well— so that the Principle was wholly unreasonable” (6). Many philosophers find that ethical, aesthetic, and metaphysical statements are in fact meaningful and that within them lies objective truth. For example, many philosophers hold to the existence of moral facts, the view that human acts are evil or good and that this corresponds (see correspondence theory of truth) to the world factually. Moreover, most philosophers agree that the scientific enterprise is itself permeated with underlying non-empirical, metaphysical assumptions.

The dagger to the heart, so to speak, for logical positivism is that its verification principle was discovered to be self-refuting: the positivist claim that “A meaningful sentence must be capable in principle of being empirically verified” appears itself incapable of obtaining empirical verification, meaning that no amount of empirical evidence can verify its foundational claim, thus rendering the verification principle a meaningless combination of words.


1. Quoted by Graham Oppy and Michael Scott (2010) in Reading Philosophy of Religion. p. 10.

2. Quoted by Graham Oppy and Michael Scott (2010) in Reading Philosophy of Religion. p. 10.

3. Quoted by Irving J. Lee (1967) in The Language of Wisdom and Folly: Background Readings in Semantics. International Society for General Semantics. p. 44

4. Carnap, R. 1934. Logical Syntax of Language. p. 8

5. Passmore, J. 1967. Logical Positivism. In The Encyclopedia of Philosophy. p. 57.

5. Craig, W. 2012. The Limits of Reason. Available.

6. Craig, W. Are There Objective Truths about God? Available.


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