PHI Searle against Turing 1

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Sheena Cummings
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1 PHI2391: Confirmation Review Session Date & Time : SMD :00-13:00 ME 14.0 General problems with the DN-model! The DN-model has a fundamental problem that it shares with Hume! Even if we drop the cases just discussed, and confine ourselves to actually true general propositions! We can generate explanations that satisfy the theory, but aren t really explanations! And we can generate things that seemingly are explanations but violate the theory Counterexamples: Flagpole! Take flagpole and its shadow! E1: laws of optics! E2: height of flagpole! E3: location of sun! From E1-3 we derive! O: The length of the shadow! The observed length of the shadow is now explained Counterexamples: Flagpole! Swap O and E2! Now we derive the height of the flagpole from the length of the shadow! Math is the same! So the deductive relationships are the same! But clearly the shadow length doesn t explain the flagpole height! DN-model doesn t distinguish simultaneous causes/effect. Counterexamples: Barometer! My barometer readings correlate with bad weather, but they don t explain it! DN-model can t handle correlation due to common cause Counterexamples: Eclipse! Since laws of celestial mechanics work backwards! I can predict backwards ( retrodict )!I then retrodict last year s eclipse on the basis of current PHI Searle against Turing 1

2 ! I can predict backwards ( retrodict )! I then retrodict last year s eclipse on the basis of current observations and the laws of mechanics! Seems a valid DN-explanation! But we don t regard this as an explanation! DN-model doesn t handle temporal aspect of causation Counterexamples: Man and pill! E1: Any one taking birth control pills will avoid pregnancy! E2: Bill took birth control pills! O: Bill didn t get pregnant! DN-Model can t distinguish relevant from irrelevant information Empirical evidence! In Baconian (experimental) science, theories face the tribunal of experience :! We need to check to see if they re true! Seems we can do so directly or indirectly! Direct Observation: trees, animals, houses; Also: measuring instruments! Indirect observation: microbes, distant stars, black holes (mathematical objects?) Empirical evidence! It is common to distinguish within our scientific vocabulary on this model! Call terms referring to observable entities the observational vocabulary! Call terms referring to unobservable entities the theoretical vocabulary Going beyond observation! Because of the presence of the theoretical vocabulary! Because science makes affirmations about remote times and places! Because logical deduction is non-ampliative (doesn t add content - think of the tautologies)! We can say that it is a general characteristic of science that it goes beyond (observational) experience! Science is underdetermined by experience. Hypothetico-deductive method a version of traditional PHI Searle against Turing 2

3 ! Hypothetico-deductive method a version of traditional scientific model! Modern formulation due to Karl Popper, Viennese philosopher of science, independent of Vienna Circle! Becomes professor at LSE after the war Falsificationism! Formulates falsificationism! View that hypotheses are proposed, tested with an aim to refuting! A scientific proposition is one that aims at being refutable! Scientific activity consists of theorising, predicting, and testing! There are crucial experiments, as the traditional view holds! We assume that the goal of an experiment (observational situation) is to test a statement called the hypothesis! Will generally be a law-like general statement (though we might in some cases test a particular hypothesis)! May or may not contain theoretical terms! Exception test/proves the rule.! Example:! H: At a constant temperature, pressure inversely proportional to volume! I1: Vol of gas = 1m 3! I2: Initial pressure: 1atm! I3: Pressure is doubled! -----! O: Volume decreases by half! Because the observation is deducible from the hypotheses + the initial observations! We say that the observation that it confirms or provides support to the hypothesis! It gives us a reason for regarding the hypothesis as (more likely to be) true Auxiliary hypotheses! Note that the terms appearing in the law are in their own way PHI Searle against Turing 3

4 ! Note that the terms appearing in the law are in their own way theoretical! We observe heat directly! But temperature is more fine-grained than mere heat! We observe it with tools - measuring instruments! So there are generally more premisses to the deduction Auxiliary hypotheses! These supplementary premisses describe the workings of the apparatus involved in the experiments! We may designate entire theories, e.g. of optics, as auxiliary hypotheses! Since they are, along with the initial state premisses, held to be true! The truth or falsity (the degree of support) of the hypothesis is taken to depend on that of the conclusion Auxiliary hypotheses! Uranus/Mercury example (pp )! Depending on circumstances, we may regard a result that contradicts an hypothesis as being! 1. A refutation of the main hypothesis! 2. A refutation of the auxiliary hypotheses! Creates room for Quine-Duhem position: an experiment never directly confirms or disconfirms a hypothesis! So there are no crucial experiments The problem of alternative hypotheses! Fundamental difficulty: whatever hypothesis an observation may confirm! We can always construct other, different hypotheses that are equally well confirmed! (Also problem of statistical hypotheses - we will not consider this) Qualitative confirmation! Opposition to/extension of the HD-model comes from the side of inductivists e.g. Hempel! Inductivists are empiricists who believe that we need inductive arguments, as opposed to merely deductive-falsificationist ones! Hempel develops theory of qualitative (as opposed to PHI Searle against Turing 4

5 ! Hempel develops theory of qualitative (as opposed to quantitative) confirmation Qualitative confirmation! Aim of theory: to provide a logic of induction! A formal characterisation of the relations that must hold between an hypothesis! And its positive instances! The concept of a positive instance proves dramatically difficult to define Qualitative confirmation! General approach is Aristotle/Hume s: I want to go from a number of cases to the general case.! In Aristotle, I would grasp an essential property or connection a cause.! In Hume, I just go from particular to general statements no real causes.! Remember difficulties with DN model (flagpole, retrodiction, etc.) Qualitative confirmation! For both philosophers, I run deduction backwards! I go from:! Premise: All Ravens are Black [( x)(rx -> Bx)]! Conclusion: f(rank) and b(ubbles) are black ravens [(Rf & Bf) & (Rb & Bb)] To:! E[vidence]: f(rank) and b(ubbles) are black ravens [(Rf & Bf) & (Rb & Bb)]! H[ypothesis]: All Ravens are Black [( x)(rx -> Bx)]! As in DN-Model, we need to define the relations between the E[vidence]-statements and the H[ypothesis] precisely.! If the definition then allows statement-patterns that we don t regard as inductively valid, that is evidence that it needs to be improved. Condition Axioms! Equivalence Condition! If E confirms H and - H H, then E confirms H PHI Searle against Turing 5

6 ! If E confirms H and - H H, then E confirms H! In other words: If the evidence supports some claim, then it supports any logically equivalent claim! So if the E supports H: The temperature of the sample was 0 C. Condition Axioms! So if the E supports H: The temperature of the sample was 0 C.! Then E supports H : The temperature of the sample was 32 F! So long as (as is the case) 0 C=32 F by definition (i.e. is analytically true) Entailment condition! If E - H, then E confirms H! H follows from E logically! So H is not just inductively supported by E, it s actually logically entailed by it, which is even stronger! So (trivially) it s also inductively supported, i.e. confirmed Special consequence condition [SCC]! If E confirms H and H - H then E confirms H! Why?! E: Frank is a black raven! H: All ravens are black! H : If Bubbles is a raven, then she is black Vs. Converse consequence condition [CCC]! If E confirms H and H - H then E confirms H! H : All ravens are black; H: If Frank is a raven, then he is black; E: Frank is a black raven.! NB (p. 51) The HD account satisfies the converse consequence condition but not the special consequence condition Hempel denies this condition. Why?! Combined with SCC, reduces to the absurd! Proof: Set E: Frank is a black raven! Set H: All ravens are black! H : All ravens are black & The moon is made of cheese! H -H! Thus by CCC, E confirms H Hempel denies this condition. Why? PHI Searle against Turing 6

7 ! Thus by CCC, E confirms H Hempel denies this condition. Why?! H -H! Thus by CCC, E confirms H! And since H - The moon is made of cheese! By SCC E confirms that! The moon is made of cheese! Hempel vs. Popper: SCC vs. CCC! Essential difference: the HD account assumes that if a hypothesis [H ] entails an observation statement [H], then anything that confirms H (for instance an instrument reading) confirms H.! Confirmation is the inverse of the deductive relation! Remember that for Popper, experiments are chosen with the aim of *refuting* (falsifying) theories. Hempel vs. Popper: SCC vs. CCC! That s why, for Popper, positive outcomes (lack of falsification) can be viewed as confirming! (Compare: You say that it s evidence for the efficacy of birth control pills that Bob did not get pregnant. This doesn t count as a positive case, because the test was not properly designed to get a refutation.) Hempel vs. Popper: SCC vs. CCC! In Hempel s account, confirmation will be the inverse of a special case of the deductive relation! We take all the objects in the observed instance! We create a specified version of the law: we restrict it to the entities involved in the observation Hempel vs. Popper: SCC vs. CCC! We restrict the law to the entities involved in the observation! If they are in conformity with the law (if it holds for them)! Then that s reason to see it as (partially) confirmed! Too complex to explain in symbolic detail see PS for the other axioms Core of Hempel s Confirmation Theory PHI Searle against Turing 7

8 other axioms Core of Hempel s Confirmation Theory! Key idea straightforward:! Take : H[ypothesis]: All Ravens are Black [( x)(rx -> Bx)]! E[vidence]: f(rank) and b(ubbles) are black ravens [(Rf & Bf) & (Rb & Bb)]! Create the specified version (the Development ) of H for E:! If Frank is a Raven, then he s black, If Bubbles is a Raven, then she s black, Core of Hempel s Confirmation Theory! If Frank is a Raven, then he s black, If Bubbles is a Raven, then she s black,! All of these are confirmed by our observations E.! So we can conclude that H is confirmed. Core of Hempel s Confirmation Theory! And, adding one more Axiom ( (Simple) Confirmation ), we can conclude that our E[vidence] confirms statements that follow logically from H, such as:! If Mary is a raven, then she is black.! And this is the very inference that we would like to be able to make. Consequences! Can be viewed as a fusion of Aristotle and Hume! We do not attain deductive certainty by grasping the necessary connection! However, by restricting the hypothesis to the class of objects under consideration,! We treat that class as if it was a representative for the total class! Which is what Aristotle called convertibility Metaphysics/Human Dependent Factors! Solution cannot be implemented metaphysics-free! Why?! I must be able to identify properties and natural kinds! Like black, green, raven, emerald etc.! Why must I be able to do this? Grue (cf. p. 54 blite ) PHI Searle against Turing 8

9 Grue (cf. p. 54 blite )! Remember the Coins my pocket example! Compare:! All the coins in my pocket are made of silver! If this penny were in my pocket, it would be made of silver! To: All copper samples conducted electricity! If this copper sample were tested, it would conduct electricity We can do the same here:! Take All emeralds examined so far were green.! And a pocketlike predicate such as grue, which applies to blue things after today, and green things up until today! It s true that All emeralds examined up until today were grue.! But we don t want to conclude that future emeralds will be grue! Because that would predict that they will be blue tomorrow. What does grue show us?! Hempel s theory of confirmation, and others like it,! Can only work if we assume something like Aristotelian kinds! Or, if we assume human-dependent factors! For instance: I can see green, but not grue! Or: There is a word for green, but not for grue (prior to our defining it) Why does this matter?! Because it shows that induction *must* involve more that just the facts! How the facts are presented matters! So, science is either partially context-dependent,! Or we must be metaphysical realists! Problems with both positions!! So: take your pick! PHI Searle against Turing 9

I. Induction, Probability and Confirmation: Introduction

I. Induction, Probability and Confirmation: Introduction 1. Basic Definitions and Distinctions Singular statements vs. universal statements Observational terms vs. theoretical terms Observational statement