Philosophy of Mind Spring 06 Francesco Orilia Lecture 5 January 31, 2006

Excursus on identity statements: basic facts  the morning star is the evening star  the morning star is a planet  John believes that the morning star is a planet   the evening star is a planet!  John believes that the evening star is a planet???  Substitutivity of identicals is OK in extensional contexts but fails in intensional contexts  MS =df last visible celestial body in the morning  ES =df first visible celestial body in the evening

Account of identity statements  “the MS is the ES” means that the individual concept THE MS and the individual concept THE ES, albeit different concepts, correspond to one entity x, in that x is the ONLY entity which has the property MS and x is also the ONLY entity which has the property ES  By saying “the MS is F” or “the ES is F”, we attribute the property F to this one entity x  But by saying “John believes that the MS is F” we are not attributing a property to x, but to the concept THE MS. We are saying that it is such that: according to John, it (the concept) corresponds to one entity that has property F. But the concept THE MS is DIFFERENT from the concept THE ES, and thus “John believes that the MS is F” does not imply “John believes that the ES is F”  Frege and Russell provide different formal accounts

Identity statements about properties  Similarly, “being water is being H20” means that the concepts WATER and H20, albeit different, correspond to the one entity h (a wordly property)  The “correspondence” in question here is probably not quite like the one involved in the morning star case (explainable with Russell’s theory of descriptions), but still it is intuitively clear  If we assume that “being water” and “being H20” stand directly for the wordly property f (rigid designation), then “is” should mean: =  If we assume that “being water” and “being H20” stand for concepts, then we must assume that “is” does not stand for =, but for the correspondence relation (call it “  ”)  The former option makes it unclear why “water is H20” is informative and “water is water” is not. I prefer the latter

The heat case  The thermodynamic concept of heat is that of a property coming in different degrees which are measurable with the mercury thermometer  The statistical mechanics concept of mean molecular energy is that of a property coming in different degrees which are measurable (roughly) by observing the speed of gas molecules  We observe systematic correlations. Consider the Boyle- Charles law of thermodynamics: kT = pV. There is an “image” in SM: 2E/3 = pV  In terms of properties: gas g has a pressure  volume pV  gas g has a temperature kT, and gas g has a pressure  volume pV  gas g has a m.m.e. 2E/3

Bridge laws postulate an identity  The observed correlation suggests a Bridge law: 2E/3 = kT  In terms of concepts: having m.m.e. 2E/3  having temperature kT  In terms of wordly properties: having m.m.e. 2E/3 = having temperature kT  Given the bridge law, we can logically derive the Boyle-Charles law of thermodynamics, kT = pV, from the SM fact that 2E/3 = pV

Use of bridge laws  (1) Observed correlation: gas g has a pressure  volume pV  gas g has a m.m.e. 2E/3  (2) Bridge Law: having m.m.e. 2E/3  having temperature kT   (3) Charles-Boyle law: gas g has a pressure  volume pV  gas g has a temperature kT (since (1) is extensional, we can substitute in it, given (2), “has a m.m.e. 2E/3” with “has a temperature kT”)  Similarly, we can logically derive other explanations/predictions about thermodinamical facts from explanations/predictions about SM facts

Why identity and reduction?  The identification of heat with m.m.e. seems to be the most plausible and economic answer to the question  Why is there this observed correlation of heat and m.m.e?  These answers are far more implausible:  It is an accident, a coincidence  There is common cause for both heat and m.m.e.  We say that heat (thermodynamics) has been reduced to m.m.e. (MS), and not vice versa, because MS has more predictive/explanatory power than thermodynamics (see E. Nagel, The Structure of Science, 1961, ch. 11, Laird Addis, The Logic of Society, 1975, Chs. 4-5, G. Bergmann, Philosophy of science, 1957)

Prediction  General law: every amount of water boils at 100 degrees C  Specific observed fact: this amount of water will have temperature 100 degree C in 1 second  LOGICALLY DEDUCED prediction: this amount of water will boil in 1 second

Explanation  Observed fact to be explained: this amount of water is boiling.  It can be LOGICALLY DEDUCED from:  General law: every amount of water boils at 100 degree C  Background condition: this amount of water has a temperature of 100 degree C  See C. Hempel, Aspects of Scientific Explanation