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Logical Positivism. Ayer on The A Priori. Language, Truth and Logic. Ayer ’ s report on what the Vienna Circle was doing, for English-speaking folk. LOGICAL POSITIVISM. What I ’ m going to do. The Vienna Circle and its historical antecedents, its influence on analytic philosophy

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Logical Positivism

Ayer on The A Priori

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Language, Truth and Logic

Ayer’s report on what the Vienna Circle was doing, for English-speaking folk.


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What I’m going to do

  • The Vienna Circle and its historical antecedents, its influence on analytic philosophy

  • The Logical Positivist program, including

    • The Verification Principle and anti-metaphysical agenda

    • Philosophy as analysis: the quest for an ideal language

    • Commitment to phenomenalism

  • Ayer on the A Priori

    • The analytic/synthetic distinction

    • Math and logic as “tautologous”

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Logical Positivism is a form of Empiricism

Thought is an independent source of knowledge.

It is characteristic of an empiricist to eschew metaphysics, on the ground that every factual proposition must refer to sense experience.

  • Problem: how to account for necessary truths, including notably truths of mathematics and logic since it’s always possible in principle to falsify empirical generalizations.

  • Ayer needs an account that will get rid of bad metaphysics without throwing out good mathematics.

No! All factual knowledge comes from experience



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The Elimination of Metaphysics

  • The Metaphysical Thesis: philosophy affords us knowledge of a reality transcending the world of science and common sense.

    • The Absolute enters into but is itself incapable of evolution and progress. (Bradley)

    • Nothing noths (Heidegger)

  • Ayer’s Thesis: talk about such a transcendent reality is, literally, meaningless.

    • “The function of philosophy is wholly critical”

    • “Philosophy leaves everything as it is.

  • The business of philosophy is analysis: “the propositions of philosophy are…linguistic in character.”

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We’re deluded by language

  • E.g. the Fido-Fido theory of meaning: every noun names an object

  • The Wino’s Paradox

    • Nothing is better than champagne

    • Thunderbird is better than nothing

    • Therefore Thunderbird is better than champagne

  • Challenge: translate this argument into thelanguage of predicate logic!

  • Russell showed that the correct analysisof the logical form of these claims blocksthe inference.

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Not your grandmother’s empiricism!

  • The old Kantian attack on metaphysics was epistemological

    • Starting from experience all we can validly infer are further facts about experience.

  • But the metaphysician can just claim access totranscendent reality via “intellectual intuition”

  • Even if “intellectual intuition” is baloney, thisdoesn’t show his conclusions are false…just that we can’t know whether they’retrue or false.

  • Logical positivists hold that metaphysicalclaims are neither true nor false but literallymeaningless—i.e. nonsense.

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The Business of Philosophy is Analysis

  • Paraphrasing away: Russell’s “On Denoting” as the paradigm of analysis

    • Nothing is better than champagne~ (∃x) (x is better than champagne)

  • Artificial languages as means to accomplish analysis

  • Logical constructions and inferred entities

    • “We are all phenomenalists now.”

  • Analysis is concerned with cognitive content understood in terms of equivalence and entailment relations.

  • Goal: the elimination of metaphysics

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Is denying metaphysics is just more metaphysics?

Wittgenstein says, "in order to draw a limit to thinking, we should have to think both sides of this limit," a truth to which Bradley gives a special twist in maintaining that the man who is ready to prove that metaphysics is impossible is a brother metaphysician with a rival theory of his own.

  • So we can’t adopt Kant’s strategy of arguing that metaphysics is psychologically impossible since that would mean showing that there are metaphysical truths that we couldn’t understand—which is itself a metaphysical claim

  • To avoid just doing more metaphysics we have to show that metaphysical claims are meaningless.

  • So we adopt the Verification Principle as a criterion for meaningfulness.

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The Verification Principle

To state the circumstances under which a proposition is true is the same as stating its meaning. (Schlick)

A sentence is factually significant to any given person, if and only if, he knows how to verify the proposition which it purports to express.

  • Example: “There’s a skunk living in the crawl space under my house.”

  • I know what experiences would verify the proposition this sentence purports to express—for example:

    • Every few days I experience a characteristic smell.

    • My dog was barking like crazy, then ran into the house yelping and whining—and stinking.

    • I saw a black and white animal in my driveway.

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Bad Metaphysics flunks the Verification Test

  • Challenge: what experiences would verify—or falsify—the following metaphysical claims?

    • The Absolute enters into but is itself incapable of evolution and progress. (Bradley)

    • Nothing noths (Heidegger)

  • Problem: what experiences would verify

    • claims about laws of nature

    • claims about the past e.g. Lucy had exactlyfour children

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Practical Verifiability & Verifiability in Principle

  • Propositions about the past can’t now be conclusively verified or falsified but we can say what sorts of experiences would verify or falsify them.

  • Verifiability doesn’t have to be feasible--only possible in principle

    • There are mountains on the other side of the moon

    • Lucy had exactly four children

  • We require only verification in principle: we have to be able to say what sort of experience would verify of falsify.

  • So propositions about the past are ok.

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Strong and Weak Verification

  • A proposition is verifiable in the strong sense iff its truth could be conclusively established in experience.

  • A proposition is verifiable in the weak sense iff it is possible to render it probable.

  • All we require for meaningfulness is weak verifiability

  • So laws of nature, which are merely very, very, very, very, very highly probable are ok.

  • Only a “tautology,” a claim which has no factual content and conveys no information about the world, can be anything more than a probable hypothesis.

    • Example: Either today is Tuesday or today is not Tuesday.

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What’s hot and what’s not


  • Ordinary empirical claims, e.g. “there’s a skunk living in my crawlspace.”

  • Claims about remote times and places, e.g. “Lucy had 4 children.”

  • Laws of nature, e.g. “under conditions found on earth, water freezes at 32 F.”


  • Metaphysics, e.g. “nothing noths.”

  • Theology, e.g. “God exists.”

  • Ethics, e.g. “Torturing young children for fun is wrong.”

  • Aesthetics, e.g. “St. Pauls, London, is one of the 10 most beautiful buildings in Europe.”

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Throwing out the baby with the bathwater?

  • The elimination of metaphysics: mission accomplished.

  • Theology as nonsense: no problem.

  • Ethics (and aesthetics) can be reconstructed as expressive or prescriptive.

  • But with math and logic…we have a serious problem.

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The Empiricist’s Math Dilemma

  • The empiricist must deal with the truths of logic and mathematics in one of the two following ways: he must say either that they are not necessary truths, in which case he must account for the universal conviction that they are; or he must say that they have no factual content, and then he must explain how a proposition which is empty of all factual content can be true and useful and surprising.

Not necessary truths!

No factual content!

J. S. Mill

David Hume

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Mill’s view rejected

The course of maintaining that the truths of logic and mathematics are not necessary or certain was adopted by Mill. He maintained that these propositions were inductive generalizations based on an extremely large number of instances.

2 + 2 = 4

Lucky for Mill things aren’t nailed down.

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Ayer goes with Hume’s Fork

“All the objects of human reason or enquiry may naturally be divided into two kinds, to wit, Relations of Ideas, and Matters of fact. Of the first kind are the sciences of Geometry, Algebra and Arithmetic... [which are] discoverable by the mere operation of thought ... Matters of fact, which are the second object of human reason, are not ascertained in the same manner; nor is our evidence of their truth, however great, of a like nature with the foregoing.” [Hume, Enquiry Concerning Human Understanding]

necessary – a priori - analytic

contingent – a posteriori - synthetic

If we take in our hand any volume; of divinity or school metaphysics, for instance; let us ask, Does it contain any abstract reasoning concerning quantity or number? No. Does it contain any experimental reasoning concerning matter of fact and existence? No. Commit it then to the flames: for it can contain nothing but sophistry and illusion. [Hume, Enquiry Concerning Human Understanding]

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Language, Truth and Logic

  • Metaphilosophy: the function of philosophy and how it accomplishes its results

  • Hume’s Fork: “Tautologies” and factual claims

    • The a priori: math and logic

    • Factual claims: science and everything else

  • Nonsense: ethics and theology

  • (Dis)solutions of traditional philosophical problems

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Kant: The Analytic/Synthetic Distinction

In all judgments in which the relation of a subject to the predicate is thought … this relation is possible in two different ways. Either the predicate B belongs to the subject A as something that is (covertly) contained in this concept A; or B lies entirely outside the concept A… In the first case, I call the judgment analytic, in the second synthetic…I merely draw out the predicate in accordance with the principle of contradiction, and can thereby at the same time become conscious of the necessity of the judgment (Kant)

  • Analytic sentences are true in virtue of language alone

  • They’re a priori (knowable independent of experience) because they’re empty of factual content.

  • They’re necessary because we don’t allow them to be false, e.g.

    • if the angles of a figure don’t add up to 180 degrees we don’t count it as a Euclidean triangle.

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A meaningful sentence is one or the other

Math and Logic

  • analytic: true in virtue of language alone. [I]t’s validity depends solely on the definitions of the symbols it contains.

  • a priori: knowable “prior to” experience

  • necessary: not logically possible that they be false

Everything else

  • synthetic: not analytic. [I]ts validity is determined by the facts of experience.

  • a posteriori (“empirical”): can only be known “after” (on the basis of) experience

  • contingent: not necessary

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Some Hard Questions

Does anything (respectable) escape Hume’s Fork?

Water is H20

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The truths of logic and math are analytic

  • Objection: If all the assertions which mathematics puts forward can be derived from one another by formal logic, mathematicians cannot amount to anything more than an immense tautology…[C]an we really allow that these theorems which fill so many books serve no other purpose than to say in a roundabout fashion A = A?

You betcha!

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Tautologous doesn’t mean obvious

The power of logic and mathematics to surprise us depends…on the limitations of our reason. A being whose intellect was infinitely powerful would take no interest in logic and mathematics.

  • We reject “truths of reason” which purport to establish facts about the world outside of language by a priori reasoning.

  • And we reject Kant’s synthetic a priori

    There is a sense in which analytic propositions do give us new knowledge. They call attention to linguistic usages, of which we might otherwise not be conscious and they reveal unsuspected implications in our assertions and beliefs.

  • The business of philosophy is analysis: to elicit those features linguistic usage and reveal entailment relations.

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A paradigmatic philosophical question

A bear walks a mile south, a mile east and a mile north—and ends up where he started. How is that possible?

We know the answer of course…

But how come it only works near the North Pole???

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It’s a question about linguistic conventions!

  • “North” and “south” trace along longitude lines which converge at the North and South poles.

  • “East” and “west” trace along latitude lines which are concentric and don’t converge;

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Who cares what games we choose…”

  • Whether a geometry can be applied to the actual physical world or not, is an empirical question which falls outside the scope of the geometry itself. There is no sense, therefore, in asking which of the various geometries known to us are false and which are true. In so far as they are all free from contradictions, they are all true…[T]he propositions of pure geometry are analytic…the reason why they cannot be confuted in experience is that they do not make any assertion about the empirical world. They simply record our determination to use words in a certain fashion.

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Summing up

  • All factually significant propositions are a posteriori (empirical)

    • Sentences which purport to be factually significant but fail the Verification Principle are nonsense.

  • A priori propositions are devoid of factual content.

    • They’re meaningful only if they’re “tautologies,” i.e. analytic.

  • A priori propositions that aren’t tautologies are metaphysical junk—a result of our misunderstanding of language

    • “Substance” comes from our “primitive superstition” that subject-predicate form reflects the structure of reality.

    • “Being” comes from the surface grammatical quirk that we express existential sentences with “is” which also does the job of predication. Existence is not a predicate!

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Some questions…

  • What is the status of the Verification Principle itself?

    • Is it an empirical claim made probable by experience?

    • Is it a “tautology” true just in virtue of the meanings of words?

  • Do analytic, a priori, necessary and synthetic, empirical, contingent line up neatly in the way suggested?

    • analytic and synthetic are semantic notions

    • a priori and a posteriori concern the way in which propositions are known

    • necessary and contingent are metaphysical notions concerning the conditions with which propositions are compatible

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More questions

  • Suppose the Verification Principle is a methodological prescription: has Ayer fiddled it to let in what he likes but exclude what he doesn’t like, i.e. metaphysics and theology?

  • Does Ayer have an adequate account of mathematics given Gödel’s proof that in any system rich enough to formalize arithmetic there are propositions which are true within the system that aren’t derivable within the system?

  • Can the distinction between analytic and synthetic propositions be made in a non-question-begging way?