(It has been a long time since I summarized Carl F. Henry, God Revelation and Authority. Here is the chapter from vol. 1, chapter 5) The Rise and Fall of Logical Positivism

Logical positivism was an important philosophical school; and its general thesis still holds a great deal of sway.  “In the early1920s the Vienna Circle propounded a criterion for verification that recognized as ‘meaningful’ only statements that are either analytic or in principle supportable by observation. All other assertations were considered ‘nonsensical’.” Carl F. H. Henry, God, Revelation, and Authority, vol. 1 (Wheaton, IL: Crossway Books, 1999), 96. An “analytic” statement is a statement which contains its own definition (more technically the predicate is contained within the subject).  The standard example of such a sentence is, “A bachelor is an unmarried man.”

The first test proposed by the logical positivists was that a statement had to be subject to “empirical verification” could be true and meaningful (we will get back to meaningful). And so since it would be possible to verify that someone who was alive had consciousness, the statement was true. But what of a person who had died? How do I verify his lack of consciousness? I can ask him but he won’t tell me.

This leads to a number of problems? How many people have to verify a proposition for it to be true?

There was a second problem with this test: it confused meaning & truth. The logical positivist conflated truth and meaning. Only true statements were meaningful. And so, a dead man has no self-consciousness is a meaningless statement.

The aim of the logical positivist was to rule out all metaphysical statements as nonsense. In particular, questions about God where put out of reach because there could be no empirical verification pertaining to God.

But this attempt to conflate verification and meaning proved unworkable. Any number of meaningful propositions can be posited which cannot be true or false, or even plain false. I can know what a false sentence means.

The whole thing caused more problems. For example, you could not assert a meaningful statement of general scientific law: how do you prove that gravity always everywhere works? And until prove that point, to say gravity does X is meaningless.

This led to a different tactic: Positivists were already in disarray when Karl R. Popper championed the principle of falsifiability as an alternative to verifiability lest ‘the radical positivist … destroy not only metaphysics, but also natural science’ (The Logic of Scientific Discovery, p. 9). By emphasizing the principle of ‘falsifiability’ Popper sought to preserve the significance of scientific laws; not empirically verified as universal explanatory principles but having survived elimination over against alternate theories, they nonetheless in principle and actuality remain falsifiable.” Carl F. H. Henry, at p. 106.

A principle of “falsification” works well enough to establish a scientific law. Gravity does X. If we some place where gravity does not X, then we can disprove the law. Since the law can be disproven, we have state a valid, and meaningful, scientific law.

But we are still left with the problem of conflating meaning and truth. And the falsification principle also created a problem with logic:

“A choice between the controversial positivist theory of meaning and the laws of logic is therefore clearly implicit: one either espouses the absurd positivist notion that while a universal affirmation makes sense, a statement denying the same proposition is neither true nor false but nonsense; or one subscribes to the logical rule that if a proposition is true, its contradictory must be false, and conversely, if a proposition is false, its contradictory must be true. Blanshard’s verdict is that ‘to give up logic itself for the sake of a controversial theory of meaning would be irresponsible’ (Reason and Analysis, p. 229) (at 110).

That might be difficult to follow, so here is a further explanation, based upon the work of C.G. Hempel, “Indeed, on the assumption that a sentence S is meaningful if and only if its negation is meaningful, Hempel demonstrated that the criterion produced consequences that were counterintuitive if not logically inconsistent. The sentence, “At least one stork is red-legged”, for example, is meaningful because it can be verified by observing one red-legged stork; yet its negation, “It is not the case that even one stork is red-legged”, cannot be shown to be true by observing any finite number of red-legged storks and is therefore not meaningful.”

https://plato.stanford.edu/entries/hempel/

So logical positivism, whether based upon verification or falsification ran into problems. But there was one final, far more damaging implication.

The propositions of logical positivism are not analytic, nor can they be verified or falsified.  How do you prove that only statements which can be verified are meaningful? You can’t find that lying around on the ground somewhere. Same with the test of falsification. Why does logical positivism get to privilege its own rules? Logical positivism as a proposition was meaningless on its own terms:

“If all propositions must be verified in sense experience, then why not the principle of verification itself? The principle is a complex of meaning, no element of which is identified with sense experience. ‘Every meaningful proposition is verifiable in sense experience.’ The predicate, ‘sense experience,’ is not sensible; it is an abstract, intelligible content; it is not identified with any given sense experience. ‘Meaningful’ is not a sense experience. What is the ‘meaning of meaning’? Whatever it might be, it cannot be identified and understood simply by pointing at something and punching it. The whole proposition might be said to stand for the totality of sense experiences and thus to symbolize them all. If this is so, then there is a ‘meaning’ beyond experience, and this ‘meaning’ is meaning itself. The amusing thing about positivism is that it proceeds to deny the intelligence by using the intelligence denied. It sets up an elaborate criterion to destroy the intellect, and the criterion turns out to be highly intellectual in structure. Positivism is, therefore, self-contradictory, self- destructive, a system that dissolves from within once it is seen to be what it is.”

F. WILHELMSEN, Man’s Knowledge of Reality, Prentice-Hall, Englewood Cliffs, N.J., 1956, pp. 49-51.