Transcript Logical Positivism Ayer on The A Priori Language, Truth and Logic LOGICAL POSITIVISM Ayer’s report on what the Vienna Circle was doing, for Englishspeaking.

Logical Positivism
Ayer on The A Priori
Language, Truth and Logic
LOGICAL
POSITIVISM
Ayer’s report on what the Vienna Circle was doing, for Englishspeaking folk.
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”
Logical Positivism is a form of Empiricism
Thought is an
independent source
of knowledge.
No! All factual
knowledge comes
from experience
Rationalist
Empiricist
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.
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.”
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 the
language of predicate logic!
• Russell showed that the correct analysis
of the logical form of these claims blocks
the inference.
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 to
transcendent reality via “intellectual intuition”
• Even if “intellectual intuition” is baloney, this
doesn’t show his conclusions are false…
just that we can’t know whether they’re
true or false.
• Logical positivists hold that metaphysical
claims are neither true nor false but literally
meaningless—i.e. nonsense.
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
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.
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.
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 exactly
four children
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.
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.
What’s hot and what’s not
Sense
• Ordinary empirical claims, e.g.
“there’s a skunk living in my
crawlspace.”
Nonsense
• Metaphysics, e.g. “nothing
noths.”
• Theology, e.g. “God exists.”
• 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.”
• 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.”
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.
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!
J. S. Mill
No factual
content!
David Hume
Mill’s view rejected
2+2=4
Lucky for Mill
things aren’t
nailed down.
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.
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]
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
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.
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
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
• necessary: not logically
possible that they be false
Some Hard Questions
Does anything (respectable) escape Hume’s Fork?
Water is H20
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!
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.
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???
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;
“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.
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!
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
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?
No!