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PHIL 4120 Lecture Notes - Truth Function, Logical Positivism, Counterfactual Conditional

Course Code
PHIL 4120
Duncan Macintosh

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Monday, March 14, 2011
Carl G. Hempel
Critique of Logical Positivism
You only understand a statement means if you understand the truth/falsity
No matter what your test is:
1. Any statement called meaningful – any truth function should also be meaningful.
(p.141) Words like “not”, “and”, “if”, etc. truth function variations. Any
statements you can build from those statements can be meaningful, if not, not
meaningful. Conjunction/disjunction (ex. If the sky is blue, something is blue).
Not meaningful shouldn’t mean anything to us
Logical Positivist (LP) Theory of Meaning
Analytic – true by meaning or definition. Truth can be known by analysis of words in
them (ex. A doe is a female deer Doe means female deer known that if a deer is
female, it is a doe)
Contingently true /Synthetically true– truth/falsity isn’t a matter of logic or definition, if
it’s false, it can be true, if it’s true it can be false (ex. Duncan wearing a jacket) Statement
about the world, beyond what you can know through logic
A statement is meaningful if it is analytic or synthetic (verify by observation, or define
what it could be to be true in a finitely long list of observations for what it means to be
(ex. Cindy is a doe what other sentences need to be true? Only if: “Cindy is a deer” is
true, and “Cindy is a female” is true. You just have to look) – may not be an observation
sentence, but can be defined in terms of observation sentences
“This board is white” – observation sentence in itself
Is this plausible?
LPs thought of themselves as making the world safe for science – all meaningful
statements could be true/false
Ex. “All storks are red-legged” – meaningful?
If true, would a finite set of observations suffice to prove it?
How many observations would you need to make to conclusively prove that all
storks have red legs?
What if there are infinitely many storks?
This sentence can’t be proven true, therefore it must be meaningless
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Any sentence built up out of this sentences therefore must be meaningless
BUT – Add “not” ex. “Not all storks are red-legged” – this sentence is verifiable
if true just need to find a stork with red legs
Ex. “For any substance there exists some solvent.”
Prove true by finite observation? need to find each substance and something
that dissolves it (could be infinitely many substances). Never be proven
Meaningless? No. Something has gone wrong.
A sentence is meaningful just incase you would know how the world would look if it was
false. If it’s false, you could prove it false. Every meaningful sentence that isn’t analytic,
you could prove it false if it was false.
Ex. “There is at least one unicorn”
There would be infinitely many observations you would need to make to prove
From any existence claim, you could not prove it
Some words stand for observable objects – some words stand for observable properties of
objects – plausible test: meaningful if non-logical terms for observable properties/objects
(nouns/verbs/adjectives) for observable objects/properties. If every word in a sentence is
meaningful, the sentence is meaningful. Any term that isn’t an observation term, can be
defined by sentences with observation terms. Meaningless if there’s even one word you
can’t define by observation terms. Meaningful if analytic or “Observation terms.” Works
great for “Dogs have hair,” “stars are bright, etc.”
What is it to define a term in observational terms?
P.17 – A scientist wants to introduce a new term – “fragility” – a property, ex. Glass, ice
are fragile, paper is not.
How to define fragility?
(D) Fx=(f)(SxT)bxt (x is fragile just incase if it were struck it would break)
Rules for ‘if then’ statements. Antecedent true, conclusion false
Rubber band can pass the test merely because it never gets struck because the test is
never performed.
Can fix by: x is fragile if it were to be struck it would break.
If this thing that would never happen, would happen, then this thing that would never
happen, would happen.
Counter-factual statements/conditional statements – have the form if x were to be true,
then y would be true. Mogul statement (refers to possibility)
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