PHIL 0610 Philosophy and Science Handout #2
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PHIL 0610
Philosophy and Science
Handout #2
Logical Positivism: Ayer
I. The Empiricist tradition
Empiricism is a group of ideas within philosophy, the basic claim of which is that the only source of knowledge is experience. In the seventeenth and eighteenth centuries, classical forms of empiricism were propounded by philosophers like Locke and Hume. We will focus on a more recent form of empiricism that arose in the early twentieth century known as logicalpositivism.
II. Logical positivism
Logical positivism is a view developed by a group of philosophers and scientists called “the Vienna Circle” that operated in the 1920s and 1930s until around the time Nazi Germany annexed Austria. The Vienna Circle was committed to bringing modern scientific methods to philosophy and every other field of inquiry.
The group believed that in order to ground an area of knowledge on a scientific footing, we must focus on the observable and the verifiable. The main goal was to eliminate meaninglessness. Various members of the Vienna Circle adopted different criteria of meaningfulness at various times, but one simple principle that has been associated with them is the verificationist principle of meaning.
The British philosophy A. J. Ayer spent a year studying in Vienna before writing Language, Truth and Logic (1936), which was the first exposition of the ideas of logical positivism published in English. That is the book from which our text is taken.
III. The elimination of metaphysics
In this paper, Ayer is attacking what he calls “metaphysics.” Ayer describes one metaphysical thesis as the claim that philosophy gives us knowledge ‘of a reality that transcends the world of science and common sense’ (p.6). Ayer claims that some statements that (bad) philosophers make (i.e., the metaphysicians) fail to have what he calls ‘literal significance.’ These are the statements that aim at something supposedly more profound than those about our ordinary experience. Ayer proposes a criterion of meaningfulness to figure out what has literal significance and what doesn’t.
IV. The criterion of verifiability
Ayer proposes a test we can use to determine whether a sentence expresses a genuine proposition about a matter of fact or fails to do so.
The criterion of verifiability: A sentence is factually significant to any given person if and only if that person knows how to verify the proposition which it purports to express.
In other words, a sentence has factual significance to an individual if she knows what observations would lead her to accept the proposition as true or reject it as false. If, on the other hand, all future experience is consistent with the sentence’s truth or falsehood (and it’s not a tautology – we’ll get to that in a moment), then the sentence is not literally significant.
To make this clearer, consider Ayer’s example sentence from a nineteenth century British idealist philosophy text: “the Absolute enters into, but is itself incapable of, evolution and progress”1
This sentence, Ayer thinks, has no factual significance. We do not know what observations would lead us to accept such a statement as true. In fact, all our future experience seems to be consistent with this sentence being true or this sentence being false. Therefore, the sentence fails to have factual significance.
Contrast this with the sentence “the population of Pittsburgh is 400,000.” We know what observations would lead us to accept this sentence as true or reject it as false. Therefore, it has factual significance.
Ayer states that some sentences might have emotional significance, but not literal significance. The sentence “Trixie is the loveliest cat” might work as an example of this kind of case. Unless I know what observations would lead me to accept it as true or reject it as false, it does not have literal significance, but it could have emotional significance for me.
Note that Ayer is careful to state that the sentence need not be actually verifiable, it need only be verifiable in principle. So, for example, the sentence “there are mountains on the far side of the moon” is in principle verifiable and therefore factually significant, even if we have no practical means of verifying it.
V. Weak vs. strong verification
Strong verifiability: A proposition is verifiable in the strong sense if and only if it could be conclusively established in experience.
Weak verifiability: A proposition is verifiable in the weak sense if it is possible for experience to render it probable.
Ayer notes that strong verifiability is implausible. A statement such as “all men are mortal” cannot be established conclusively by experience. Since the claim is that “all” men have some property, we would be unable to conclusively establish such a claim on the basis of any finite series of observations.
VI. Analytic sentences
Mathematical truths pose a special case for the logical positivists. The claims of mathematics are usually not the kinds of statements for which we can give verifiability conditions. However, they do want to keep mathematical statements within the category of meaningful and not metaphysical claims.
To deal with this case, we need to distinguish between analytic and synthetic sentences. Some sentences are true or false just in virtue of the meanings of the words in the sentence. For example, the sentence “all bachelors are unmarried” is true in virtue of the meanings of the words in the sentence. The sentence “all bachelors have a beard” is an example of a synthetic sentence. Whether it is true or false depends on how the world is and not just the meanings of the words.
According to Ayer, all of mathematics is composed of analytic sentences. Any claim in mathematics, according to this way of thinking, trades on the meanings of the terms involved and is thus empty of content relating to the world. Mathematical statements are literally significant, although they lack factual content. This distinction allows us to clarify Ayer’s definitions a little further.
Recall from earlier: The criterion of verifiability: A sentence is factually significant to any given person if and only if that person knows how to verify the proposition which it purports to express.
Putting these ideas together, a sentence is literally significant if it is factually significant or if it is a tautology (i.e. an analytic truth).
VII. Science!
So what does all this have to do with science? According to Ayer, scientific knowledge is the paradigm of knowledge. He is using what he takes to be the normal way of conducting science and applying it to philosophy, which he thinks is a bit of a mess. Verificationism is what he takes to be at the heart of doing science.
2023-02-18
Logical Positivism: Ayer