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PHIL 4120 (9)

Carl G. Hemple

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PHIL 4120
Duncan Macintosh

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 true) (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 • 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 false • 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
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