Alfred jules ayer

See <a class=’internal-link’ href=’/Notes-on-Ayer’s-Verification-Principle’>Notes on Ayer’s Verification Principle</a>

Alfred Jules Ayer (1910–1989)’s main writing is Language, Truth and Logic.

He became the British representative of Logical Positivism, by bringing this philosophy to his country, UK, for the first time in history.

Very influenced by Bertrand Russel since early age, in particular interested in his skepticism: this argument followed him during all of his career. No argument should

Also influenced by Gilbert Ryle, who introduced him to the founder of the Vienna Circle, of which he then became the only British member.

The principle of Verifiability

We say that a sentence is factually significant [meaningful] … if, and only if, [we know] how to verify the proposition which it purports to express – that is, […] what observations would lead [us], under certain conditions, to accept the proposition as being true, or reject it as being false.”

First of all, sentences have to be verifiable in principle. A focus on the factual verifiability.


there are mountains on the farther side of the Moon

This sentence at Ayer’s time wasn’t practically or actually verifiable, yet it was conceivable as a logical possibility.

For a statement to be verifiable it’s sufficient for it to be potentially verifiable.

Logically, Truth comes after verification, which subsequently occurs empirically.

Plainly we all understand, in many cases believe, propositions which we have not in fact taken steps to verify. Many of these are propositions which we could verify if we took enough trouble. […] A simple and familiar example of such a proposition is the proposition that there are mountains on the farther side of the moon. No rocket has yet been invented which would enable me to go and look at the farther side of the moon, so that I am unable to decide the matter by actual observation. But I do know what observations would decide it for me, if, as is theoretically conceivable, I were once in a position to make them. And therefore I say that the proposition is verifiable in principle, if not in practice, and is accordingly significant.

We focus on what it’s possible to verify

An example of an unverifiable statement is God works in mysterious ways. We’re not attempting to prove the existence of God but for this statement we can’t state what is actually true or false: the statement is meaningless

Strong and weak verifiability

Conclusive verifiability

the meaning of a proposition is the method of its verification

Schlick, Meaning and Verification

[…] if we accept conclusive verifiability as our criterion of significance, as some positivists have proposed, our argument will prove too much. Consider, for example, the case of general propositions of law – such propositions, namely, as arsenic is poisonous; all men are mortal; a body tends to expand when it is heated. It is of the very nature of these propositions that their truth cannot be established with certainty by any finite series of observations.

Universal vs. Historical propositions;
strong and weak statements

Weak verifiability

A proposition is said to be verifiable, in the strong sense of the term, if, and only if, its truth could be conclusively established in experience. But it is verifiable, in the weak sense, if it is possible for experience to render it probable.

Statements may only be highly probable: the stronger type of verification is actually too strong. A weaker link is enough to assert verifiability.

Accordingly, we fall back on the weaker sense of verification. We say that the question that must be asked about any putative statement of fact is not, Would any observation make its truth or falsehood logically certain? But simply, Would any observations be relevant to the determination of its truth or falsehood? And it is only if a negative answer is given to this second question that we conclude that the statement under consideration is nonsensical.

Relevance is not used with a specific logical meaning, it relies on interpretation. Nevertheless, its meaning is univocal. The introduction of the term “relevant”

‘weak’ verification […] cannot be prevented from opening the gates for any statement, however meaningless, to enter, provided that someone can be found to claim that observation is in some sense relevant to it. As a criterion for distinguishing sense from nonsense relevance plainly does not work: indeed to accept it is in effect to abrogate the principle of verification altogether.

I. Berlin, Verifiability in Principle, Proceedings of the Aristotelian Society, XXXIX, 233.

Ayer understands this counterargument, together with the many others he received.

Eventually, the theory itself becomes doubtable. There doesn’t seem to be a test to verify this very method. The verifiability of a sentence becomes therefore exactly the type of metaphysical problem that Logical Positivists strongly avoided.

We can’t axiomatically accept the verifiability principle since it can’t even prove or explain its meaningfulness itself.

Next topic: Peter Frederick Strawson



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