Language, Truth, and Logic by A.J. Ayer


Alfred Ayer (1910-1989), introduced the philosophy of logical positivism to the UK in his book Language, Truth, and Logic (1936).

Logical positivism was the brainchild of a the Vienna Circle, mathematics, philosophers and scientists who met in Vienna to discuss scientific methodology and language. Their basic beliefs covered several ideas: that the logical structure of any scientific theory could be elicited apart from its content and that meaning is only verifiable through experimentation and observation. They assumed a doctrine of unified science in which there were no real differences between the physical and the biological sciences or the natural and the social sciences. Their conclusion was that statements of morality, aesthetics and religion were meaningless. 

Logical positivism differed from earlier forms of similar philosophies, such as the empiricism and positivism of Hume and Ernst Mach, because it held that the basis of knowledge was public verification rather than personal experience. It differs from the philosophies of Stuart Mill and Comte in that metaphysical doctrines are not considered false but meaningless. This implies that the questions of substance, causality, freedom and God are not real questions.

The question of God was understood as a theory about language, not Nature, since all Vienna Circle criticism is about language and designed to demonstrate the unity of science, expressible in a single common scientific language.

As World War II approached, in 1938 the Circle was subject to political pressure and its members disbanded.

In 1932 Ayer travelled to Vienna to study under the founder of the Vienna Circle group, Moritz Schlick. There he became interested in logical positivism as an advance in the tradition of empiricism and wrote Language, Truth, and Logic, as a summary and defense of logical positivism, arguing for the verifiability principle of experience. He called his version of the theory "logical empiricism".

Ayer explains his influences in the Preface to his 1936 book: Berkeley and Hume which were followed in logic by Russell and Wittgenstein. However, he is critical of the empirical tradition and outlines his own empirical views. He accepts Hume's distinction of of genuine propositions into logical and empirical together with the principle of verification which requires observation to determine its truth or falsehood. This has far-reaching consequences for his later thinking:

"To test whether a sentence expresses a genuine empirical hypothesis, I adopt what may be called a modified verification principle. For I require of an empirical hypothesis, not indeed that it should be conclusively verifiable, but that some possible sense-experience should be relevant to the determination of its truth or falsehood."


In a society of competing narratives language has a central role. Ayer's challenge is how to decide the validity and accuracy of accounts: are they rhetoric or fact-based? He argues that if statements are not based on observations or experience then they are meaningless.

The three main ideas in Language, Truth, and Logic are:

- meaningful statements are verifiable or analytically true and anything not observable or testable has no meaning.

- metaphysical or existential claims which have no empirical evidence are nonsensical. 

- logical positivism advocates a scientific approach to knowledge through analysis and rejects subjective interpretations, or appeals to intuition.

Ayer extends the criterion of verifiability by presenting the problem of synthetic statements. These go beyond information gleaned through logic and they need empirical evidence as verification. He argues that a synthetic statement must be able to be reduced to elementary statements that directly describe observable facts. He presents the example: "The cat is on the mat." It can be reduced to two elemetary statements: "There is a cat." and "The cat is on the mat." As both of these simple statements are verifiable through observation, the synthetic statement is recognised as meaningful.

The author also discusses tautologies and contradictions. The tautological statement is true by definition. For example "A bachelor is an unmarried man" is accepted as true since bachelor and unmarried man are tautologico. On the contrary, contradictions are always false. For example, "A square circle exists" is a contradiction because the concept of a square circle is self-contradictory.

Ayer then addresses the problem of meaning in ethics and aesthetics which are statements of emotion or personal preferences, are subjective and cannot be objectively verified. For example "Chocolate ice cream is delicious" is the expression of a personal preference, and not objectively provable. In the same way "Lying is morally wrong" is a moral sentiment, not verifiable through observation or logical analysis. 

(Faced with a society which encourages more and more personal narratives Ayer's criterion insists on the importance of empirical evidence and logical analysis to determine the meaningfulness of these statements.)



Ayer believes that the function of philosophy is not a search for first principles, as was the tradition from the ancient Greeks, but critical analysis, without reference to metaphysics:

“The philosopher as analyst is not concerned with the physical properties of things, but only with the way in which we speak about them.”

He argues that philosophy does not offer explicit definitions, but definitions in use. He affirms that perception consists in logical constructions from sensory data. This implies that philosophical proportions are not empirical but deal with the logic outcomes of linguistic conventions.


Ayer rejected metaphysical thinking, preferring what he called verifiability. This meant that propositions were meaningful only if they could be empirically verified. However, he recognised that no statement can be conclusively confirmed, only supported by observations to determine its falsehood or truth. This implies that he rejects the kantian notion of synthetic a priori propositions. (Example: “Some bodies are heavy” is a synthetic statement because the notion of heaviness is not necessarily contained in that of bodies. However, “All husbands are male” is an analytic proposition because maleness is contained in that of husband.) 

Ayer insisted that no general proposition about a fact can be known to be absolutely valid. He contended that the function of the words 'true' and 'false' in a statement was to signal assertion or negation. However, no empirical propositions are certain, including those referring to immediate experience.

The author also disagreed with Stuart Mill that logical and mathematical statements were inductive generalisations. He emphasised that they were necessarily true because they were analytic, meaning not that they offered new knowledge, but that they shed light on linguistic usage. 


Ethics and theology are considered assertions of values by the author. He claims that their assertions are "emotive". Therefore they are neither false nor true, but sentiments.

As regards theology it is not possible to demonstrate God's existence, or even its probability. Asserting the existence of a transcendent God is a metaphysical statement and therefore meaningless.


Ayer criticises metaphysics, arguing that it fails to meet the rule of the literal meaning of language and so is meaningless. Meaning, for the author, relies on being able, through observations, to accept a proposition as true or false. 

However, Ayer qualifies verifiability by distinguishing 'practical' verification and verifiable 'in principle'. The second case depends on the present state of science. Theoretical physics, for example, is acceptable as meaningful since it might be verified in the future.

Another distinction is between strong and weak verifiability. The Vienna Circle insisted on a strong interpretation which required conclusive empirical verification for meaningfulness. In the weak theory, chosen by Ayer, meaningful meant that experience made the conclusion probable. He elected the weak theory arguing that no empirical statement is 100% conclusively demonstrable. He suggests that metaphysical thinking has been misled by placing a generalisation, "Being", as the subject of a sentence, instead of a concrete, literal subject. 

(Lakoff, a cognitive linguist, in Philosophy  in the Flesh) suggests that categories belong to the metaphor 'categories are containers'. He traces this metaphoric thinking to Aristotle's categorisation of 'Being', arrived at by studying the world through language which he thought reflected the categories of mind.

In On the Origin of Time, Thomas Hertog, a collaborator of Stephen Hawkings, statea that the theoretical physicist, reformed his view of the universe from the God's-eye view to the worm's-eye view, that is, from the out-of-the-box, omniscient perspective to one from inside the universe-container.)


Ayer published his book The Problem of Knowledge in 1957. He put forward three guarantees for knowledge: self-evidence; truth supported by experience; valid claims from deduction.

The author argued that the problem of knowledge was the result of philosophers' emphasis on conditions for belief faced with philosophical scepticism and relativism. He believed that reliability is enough for knowledge even when there is no response as to how the information is known.

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