PHILOSOPHY OF LANGUAGE
VERIFICATIONISM – AYER AND HEMPEL
LECTURE
PROFESSOR JULIE YOO
Motivations for Verificationism
Emotive vs Cognitive Meaning
Analytic vs Synthetic Sentences
Terminology
Synonymy and Analyticity
Intension and Extension
Criteria of Cognitive Significance
Verifiability
Reductionism and Foundationalism
Ayer’s Approach
Practical vs In Principle Verifiability
Conclusive vs Probably Verifiability
Direct vs Indirect Verifiability
Applying Ayer’s Criterion
Problems with Ayer’s Criterion
Observational Base
Relation Between Observation and Theoretical Sentences
Criteria for Meaningful Constituent Terms
Hempel’s Approach
Constraint on Criteria for Cognitive Significance
Verifiability Requirement (VR)
CS As Definability from Observational Terms
Requirement of Definability
Verificationism – Ayer and Hempel
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MOTIVATIONS FOR VERIFICATIONISM
Here are some questions that might have crossed your minds: Why can’t philosophy settle longstanding disputes about ontology – nominalism vs realism, the existence of possibilia, the
existence of God, whether change is essentially an illusion, whether everything is “one,” whether
life has a meaning, the nature of moral goodness, the nature of beauty, the nature of truth –
things we really care about? Why isn’t there any progress in philosophy? Why are we still
talking about the same issues philosophers were talking about 2000 years ago?
Philosophers of a strong empirical bent, such as Hume, had a fairly low opinion of how much
philosophy could accomplish in these traditional arenas. Hume’s own view was that such
questions take us beyond what we actually experience, and so draw us to a domain where
nothing can be settled by deductive or inductive reasoning. Such scorn for traditional
metaphysics is nothing new – philosophers are the best anti-philosophers – and its most
vociferous critics were the early 20th century philosophers of the Logical Positivist movement:
Ayer, Schlick, Carnap, Hempel, and Neurath.
Their overarching goal was to separate those philosophical questions that could be answered
from those that could not ever be answered. The pursuit of this goal led them to examine the
nature of a meaningful sentence, for if a criterion of meaningfulness could be determined, then
we could apply this criterion to philosophical statements to gauge their worth. Empirical
verifiability was the condition they landed upon. The ones that are meaningful according to the
criterion would be the ones whose truth we could empirically confirm or verify. The ones that
were not meaningful would be the ones whose truth we could not empirically confirm or verify.
The movement of philosophy that embraced this criterion of meaningfulness and the approach to
doing philosophy is now known as Verificationism.
If verifiability were to function as the criterion, then much of metaphysics would have to be
deemed unworthy since metaphysical claims can’t be confirmed. It’s not that we aren’t smart
enough. Rather, metaphysical claims make us violate or ignore rules of semantic meaning. As a
result, verificationism denounces as meaningless large bodies of sentences, such as religious
statements about the afterlife and philosophical statements about possible worlds, just to mention
a few. For example,
After we die, our souls go to heaven, if we lived a good life.
Although this sentence sounds meaningful – it’s a perfectly grammatical sentence, and it
manages to communicate a thought – it isn’t meaningful according to Verificationism. The
reason is that it there are no possible conditions under which any person can confirm or
disconfirm its truth, since no one can die, check out the afterlife scene (if there is on), and come
back to tell us about it. But what is it for a sentence to be verifiable or confirmable? Let us first
get a sense of how Verificationists taxonomized types of expressions.
Verificationism – Ayer and Hempel
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Expressions
Unmeaningful / Unverifiable
religious and metaphysical claims
Meaningful
Emotive Meaning
Cognitive Meaning
Analytic
a priori
necessary
Synthetic
a posteriori
contingent
Emotive vs Cognitive Meaning
A sentence S is cognitively meaningful or is cognitively significant (CS) if it can have a truthvalue. They have “factual content” or “empirical content.”
A. The cat is on the mat.
B. There are rings around Saturn.
C. All swans are white.
A sentence can also have a different kind of meaning, an “emotive meaning,” if it expresses a
value judgment. These sentences make ethical claims, aesthetic claims, and other judgment
claims:
D. Capital punishment is wrong.
E. We all ought to be vegetarians.
F. The Mona Lisa is beautiful.
According to Verificationists, these kinds of statements don’t have “factual content.” Instead,
express a feeling or an emotion. The main concern for Verificationists was to come up with a
criterion of cognitive meaningfulness, and this amounted to coming up with a suitable Principle
of Verification. How the principle should be stated, however, was none too easy, as we see with
Hempel’s three attempts. But before we get there, we need to cover some distinctions that play
an important role in Verificationist Theories of meaning. All cognitively significant sentences
were either analytic or synthetic.
Analytic vs Synthetic Sentences
S is analytic (analytically true or false) IFF its truth-value depends only upon the meanings of the
words in S:
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G. All bachelors are unmarried.
H. Of P is true, then not-P is false.
I. 5 + 7 = 12
The truth-values of G, H, and I don’t upon how the world is; G would still be true even if all the
bachelors in our world disappeared. According to the Verificationists, we can know the truth of
analytic sentences a priori and their truth-value is necessary.
S is synthetic (synthetically true) IFF its truth-value depends upon how the world is and also the
meanings of the words in S:
J. Grass is green.
K. Temperatures go down to below freezing in December in PA.
L. Easton has just one college.
These sentences are true not only because of what the words express, but because what the words
express corresponds to how the world is. We can know the truth of synthetic sentences only a
posteriori and their truth-value is contingent. (The same goes for synthetically false sentences;
their falsity is a function of what the words mean.)
TERMINOLOGY
Synonymy and Analyticity
Terms that have the same intension are synonyms. They are related definitionally, or in
philosophical parlance, they are related analytically. What, exactly, is an analytic statement?
We have many examples:
a.
b.
c.
d.
Bachelors are unmarried.
Widows were once married.
A sister is a sibling.
A vixen is a female fox.
Intension and Extension
“Meaning” is used to mean either the intension of a term or the extension of a term, and it is a
distinction that applies both to singular terms as well as general terms. A term’s intension is
what a Fregean would call its sense, or what we could call its connotation: it is the set of
concepts or descriptions we grasp. A term’s extension is what a Fregean would call its reference,
or what we would call its denotation: it is the actual thing or stuff that is picked out by the term.
As we saw, two terms may have the same extension but different intensions:
cordate = intension creature with a heart
renate = intension creature with a kidney
cordate = extension renate
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water = intension the odorless, tasteless, liquid that fills our lakes and rivers, …
H2O = intension the chemical compound made up of two hydrogen , …
water = extension H2O
In our study of reference, we also encountered the converse of this relation: two terms have the
same intension but different extension:
water (earth) = intension water (twin earth)
water (earth) ) = extension H2O
water (twin earth) = extension XYZ
CRITERIA OF COGNITIVE SIGNIFICANCE
Verifiability
Analytic sentences are verifiable simply by consulting the meanings of the words contained in
the sentence. Analytic sentences, according to Verificationists, did not convey any information
about the world. They were just restatements of definitions. It is synthetic sentences that
interested Verificationists, since these are the only kinds of sentences that convey any
information about the world.
It is synthetic sentences that interest Verificationists, since these are the only kinds of sentences
that can convey any information about the world. In other words, they are the only kinds of
sentences that have any substantive content. The core idea is this: a sentence is meaningful only
if its truth-conditions can be verified. If a sentences has no conditions for verification – if there
are no empirically identifiable circumstances under which the sentence can be conformed as true
or disconfirmed as false – then the sentence is not meaningful. → Q2
(VR) S is cognitively significant (CS) IFF S is verifiable by experience.
This is a very rough formulation of the principle we wish to capture. Not all of our sentences are
reports of our experiences or observations. Those that do report such things are ‘observation
sentences” (SO).
M. There is a green patch in my visual field.
N. The liquid tastes salty.
O. The oscilloscope is reading out sine waves.
But many of our sentences express things that go beyond our immediate experiences. These are
called “theoretical sentences” (ST).
P. Electrons have negative charge.
Q. Energy is quantized.
R. Matter is composed of strings.
The entities referred to by P, Q, and R, as well as others such as protons, quarks, black holes, the
event of the Big Bang, and countless others, are either too small, too far away, or simply in the
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past (or future). Since these things can’t be observed directly, how can sentences about these
entities be meaningful?
Reductionism and Foundationalism
Verificationists had something like the following model in mind. Theoretical sentences are CS
because they are ultimately reducible to observation sentences. Either they are definable in
terms of observation sentences or they are derivable from observation sentences or they are
translatable in terms of observation sentences:
ST is CS (meaningful) if
a. ST is definable in terms of a set of SO, or
b. ST is derivable from SO, or
c. ST is translatable in terms of SO
+
THEORETICAL
ST
ST
ST
ST
ST
ST REDUCIBLE TO SO
SO
SENTENCES
SO
ANALYTIC REDUCTION
ST
SENTENCES
SO
OBSERCATIONAL
SENTENCES
SO REPORT
EXPERIENCE
EXPERIENCE
EXPERIENCE
__________________________________________________________________
THE WORLD
And of these claims, some are CS even though they can‘t be verified given our technological or
physical limitations, or verified conclusively, or verified directly. How can we draw up a
criterion so that these sentences come out meaningful, but typically metaphysical statements
don’t come out meaningful?
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AYER’S APPROACH (FROM LTL)
Here is Ayer’s Criterion of Cognitive Significance:
S is CS IFF S is verifiable by experience, where
a. S is in principle verifiable
b. S’s verification renders S more or less probable
c. S is verifiable either directly or indirectly
Practical vs In Principle Verifiability
S is practically verifiable for A if A has the practical means to place herself in a situation that
would enable her to verify S.
S is in principle verifiable for A if S isn’t practically verifiable, but A can theoretically conceive
of a situation she could be in to verify S.
EX:
Jane has more than $10 in her bank.
A lemon contains acid.
→ practically V
→ practically V
Pluto has nitrogen in its atmosphere.
We can travel back in time.
→ in principle V
→ in principle V
Conclusive vs Probable Verifiability
S is conclusively verifiable if there are observation sentences O1, O2, …, On such that either
O1, O2, …, On ├ S
OR
O1, O2, …, On ├ not-S
S is probably verifiable if there observation statements O1, O2, …, On such that either
p(S / O1, O2, …, On, T ) > p(S / T)
EX:
OR
Jane has more than $10 in her bank.
Pluto has nitrogen in its atmosphere.
p(S / O1, O2, …, On, T ) < p(S / T)
→ conclusive V
→ conclusive V
All metals expand when heated.
→ probable V
A person would get crushed in a black hole. → probable V
Direct vs Indirect Verifiability
S is directly verifiable if “it is either itself an observation statement, or is such that in conjunction
with one or more observation statements it entails at least one observation statement which is not
deducible from these further premises alone.” (Ayer)
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S is indirectly verifiable if “it satisfies the following conditions: first, that in conjunction with
certain other premises it entails one or more directly verifiable statements which are not
deducible from these other premises alone; and secondly, that these other premises do not
include any statement that is not either analytic, or directly verifiable, or capable of being
independently established as directly verifiable.” (Ayer)
Applying the Criterion
→ Q3 Explain how you could apply the criterion of significance to the following sentences or
hypotheses to determine whether they are meaningful:
S. Mars is closer to the sun than Pluto.
T. The soul is indivisible.
(S) is cognitively significant. Even though Mars and Pluto may not be directly observable with
the naked eye, we can observe images projected by telescopes. So statements about Mars and
Pluto can ultimately be reduced to statements about telescopic images, instrument readings, and
mathematical calculations.
(T) is not cognitively significant. Souls, no matter how much we try, are not observable entities.
They aren’t physical so they are not detectable by any of our senses. So there are no observation
sentences to which (T) can be reduced.
PROBLEMS WITH THE CRITERION
Observational Base
→ Q4 If observation sentences are to do their job, they must be infallible or incorrigible. But
we buy this at the price of scientific realism. Only solipsistic statements can be incorrigible: “I
am experiencing a green patch in my visual felid now,” “There is a table in from of me now.”
But this is hardly what we thought would serve\ as the proper foundation for science (pace
Descartes). This kind of project has been called “psychologism,” “phenomenalism.” “idealism,’
“methodological solipsism.”
Relationship between SO and ST
The goal, according to Hempel, is to “characteriz[e] in a precise manner the relationship which
obtains between a hypothesis and one or more observation sentences whenever the phenomena
described by the latter [i.e., observation sentences] either confirm or disconfirm the hypothesis in
question.” (p 27, bottom L – top R). Observation sentences express observable evidence.
Hempel goes over several different ways of specifying the relation:
1. Testability Criteria
i. Verifiability Requirement (VR)
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ii. Falsifiability Requirement (FR)
iii. Ayer’s Proposal
2. Criteria for Constituent Terms
3. Interpreted Systems
But each attempt faces insurmountable problems. The Testability Criteria, as stated, are too
strong because no universal statements or references to historical events are fully testable. If we
try to weaken this so that there is only an evidential connection between observation statements
and theoretical ones, then it becomes too weak.
→ Q5 Consider the Criteria for Meaningful Constituent Terms. Instead of trying to specify
inferential connections between SO and observation hypotheses (HO), this strategy tries to specify
the vocabulary for cognitively significant sentences. This amounts to an attempt to specify
criteria for cognitively significant terms. The idea here is that a terms is CS if it can be defined
in terms of the basic vocabulary for cognitively significant sentences, a vocabulary that is made
up of observational terms that are either general or singular.
1. Observational General Terms: Terms that refer to some observational property or
relation.
EX:
“blue”
“happening at the same time as”
“shiny compound”
2. Observational Singular Terms: Terms that refer to some observational particular or
“physical object of macroscopic size,” (Hempel p. 30).
EX:
“the needle reading of this instrument at time t”
“the moon”
“the Hubble telescope”
Criterion for Meaningful Constituent Terms: S is CS IFF the definiens of S contains only
observational general terms or observational singualar terms and logical vocabulary.
This is too strong because it cannot account for dispositional terms, which are CS. These are
terms like “soluble” “fragile,” “electrical conductor.” The problem is that dispositions can
t be directly observed. The fragility of a vase, for instance, can’t be observed since it needs to be
struck and then shattered in order for it to have the property of fragility.
→ Q6 Consider, finally, the strategy of Interpreted Systems. A guiding assumption for the last
two strategies was that a sentence could be confirmed or disconfirmed in isolation from its
connection with other sentences of the theory of which that sentence is a part. This is called
confirmation atomism, because the idea is that each sentence in a theory is a unit unto itself that
can be confirmed or disconfirmed without the help of other background hypotheses that make up
the theory. Moreover, its confirmation or disconfirmation has no repercussions for the other
sentences that make up the theory of which it is a part. But as we will see, this picture of
confirmation is naïve.
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HEMPEL’S APPROACH
Hempel’s goal is to “characteriz[e] in a precise manner the relationship which obtains between a
hypothesis and one or more observation sentences whenever the phenomena described by the
latter [i.e., observation sentences] either confirm or disconfirm the hypothesis in question.” (p 27,
bottom L – top R).
O1, O2, …, On
?→?
H
And what kind of relation can H bear to O? Observation sentences express observable evidence.
We wish to determine whether some hypothesis H is meaningful. H is meaningful if its truth
condition is directly observable or follows from other sentences whose truth conditions are
directly observable. This is what confers “cognitive significance.”
Constraint on Criteria for Cognitive Significance
By “cognitive significance,” or “empirical significance” Hempel means whatever it is that makes
a synthetically true (or false) sentence meaningful. The goal is to come up with criteria that
determine the meaning of a synthetic sentence. But surely not any criterion will do. We need
some constraints on what can count as good or appropriate criteria. Hempel gives us
“requirement (A).” → Q 1 If some hypothesis H has no cognitive significance, then no
logically complex sentence that containing H is cognitively significant (e.g., If H then P, if P
then H, ~H, H and P, H or P.)
Verifiability Requirement (VR)
According to this theory, a sentence is meaningful only if its truth can be verified. If a sentence
has no conditions for verification – if it can’t be confirmed or disconfirmed under any possible
circumstances – then the sentence is not meaningful. → Q2
VR
S is cognitively meaningful IFF S is verifiable, i.e. can be confirmed or
disconfirmed by observable evidence.
But there are degrees and strengths of verifiability, and some sentences have truth conditions that
aren’t directly observable. What should we do about these?
CS As Definability from Observational Terms
→ Q5 Instead of trying to specify inferential connections between observations sentences and
hypotheses, this strategy tries to specify the vocabulary for cognitively significant sentences.
This amounts to an attempt to specify criteria for cognitively significant terms. We have one of
two possibilities to consider.
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Requirement of Definability
The idea here is that a term is CS if it can be defined in terms of the basic vocabulary for
cognitively significant sentences, a vocabulary that is made up of observational terms that are
either general or singular (see above). The problem, though, is that this is too strong because it
cannot account for dispositional terms. These are terms like “soluble,” “fragile,” “electrical
conductor.” The problem is that dispositions can’t be directly observed. The fragility of a vase,
for instance, can’t be a observed since it needs to be struck and then shattered in order for it to
have had the property of fragility.
INTERPRETED SYSTEMS
→ Q6 A guiding assumption for the last two strategies was that a sentence could be confirmed
or disconfirmed in isolation from its connection with other sentences of the theory of which that
sentence is a part. This is called confirmation atomism, because the idea is that each sentence in
a theory is a unit unto itself that can be confirmed or disconfirmed without the help of other
background hypotheses that make up the theory and that its confirmation or disconfirmation has
no repercussions for the other sentences that make up the theory of which it is a part.
Core Idea:
Problem:
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