extension / intension

254

qualities of experiences are, at bottom,qualities states or objects are represented aspossessing (Harman, 1990; Lycan, 1996).

Other opponents of the “act–object”model of experience have suggested thatexperiences are analyzable adverbially (seeChisholm, 1966, ch. 6). In experiencingsomething red, you are not encountering a private red object, you are experiencing“redly.” You could experience in this wayeven if nothing at all in you or in yourvicinity is red.

Although such conceptions of experiencedispense with a special class of sensoryobject, it is not clear that they thereby avoidthe mind–body puzzles associated with traditional act–object theories. It is difficultto resist the thought that there remains an ineffable “something it is like” to experi-ence a tomato visually. This “something,”whether a feature of a private object or of an“experiencing,” seems invariably to be left out of objective “third-person” accounts of the material world however exhaustive( Jackson, 1982). In response, materialistscontend there is good reason to supposethat “subjective” qualities are, at bottom,nothing more than unmysterious physicalproperties of sentient creatures, the subjective–objective divide reflecting only an unre-markable difference between being in anexperiential state and observing that state.

bibliography

Chisholm, R.M.: Theory of Knowledge (Engle-wood Cliffs, NJ: Prentice-Hall, 1966).

Harman, G.: “The Intrinsic Quality ofExperience,” Philosophical Perspectives 4(1990), 31–52.

Jackson, F.C. (1982) “EpiphenomenalQualia.” The Philosophical Quarterly 32,127–36.

Lycan, W.G.: Consciousness and Experience(Cambridge, MA: MIT Press, 1996).

McDowell, J.: Mind and World (Oxford: OxfordUniversity Press, 1994).

Nagel, T.: “What Is It Like to Be a Bat?,” ThePhilosophical Review 83 (1974), 435–50.

Peacocke, C.: “Nonconceptual Content:Kinds, Rationales, and Relations,” Mind andLanguage 9 (1994), 419–30.

Price, H.H.: Perception (London: Methuen,1932).

Sellars, W.: “Empiricism and the Philo-sophy of Mind,” Minnesota Studies in thePhilosophy of Science, vol. 1, ed. H. Feigl andM. Scriven (Minneapolis: University ofMinnesota Press, 1956), 253–329.

Smart, J.J.C.: “Sensations and Brain-processes,” The Philosophical Review 68(1959), 141–56.

john heil

extension/intension The extension of anexpression is the object or objects to whichthe expression applies. For example, theextension of the noun “rose” is the collec-tion of all roses, and the extension of thedefinite description “the number of planets”is the number 9. Some hold that the exten-sion of a (declarative) sentence is its truthvalue. The intension of an expression is itsmeaning.

The semantic analysis of natural languagecalls for a sharp distinction between exten-sion and intension. Many different definitedescriptions may describe the same object – and hence have the same extension. For example, “the number of planets”, “thesuccessor of 8”, “the number of a cat’slives” (according to myth), all have as theirextension the number 9; and they all differ,not only in vocabulary, but in meaning, in intension. Furthermore, many meaningfulexpressions lack extension. For example,the predicate “cat with nine lives” (literallyspeaking) and the definite description “thelargest number” have this property. More-over, the extension of an expression canvary over time (and with respect to otherparameters) without the expression chang-ing in meaning. The extension of the predic-ate “rose” changes as old roses fade and newones bloom, but the word does not changein meaning.

These examples show that there is such athing as the extension/intension distinction.What to make of it is another matter. Thecases of “same extension, different inten-sion” are compatible with the principle thatexpressions with the same intension musthave the same extension; but this principle

9780631199991_4_P2005.qxd 1/12/09 3:06 PM Page 254

extension / intension

255

may seem to conflict with the examples of uni-vocal expressions with varying extensions.The disparity is resolved if the principle is revised to assert that expressions with the same intension have the same rangeof extensions with respect to extension-determining factors such as the passage oftime. Call this version of the principle “IDE”(“intension determines extension”).

Coextensive expressions with differentintensions cannot in general be substitutedfor one another within an expression ewhile preserving the extension of e (assum-ing that the extension of a declarative sen-tence is its truth value). For example, Jonesmight believe that 9 is divisible by 3 and yetnot believe that the number of planets is divisible by 3. Hence, substituting “thenumber of planets” for “9” in the true sentence

(1) Jones believes that 9 is divisible by 3.

results in the false sentence

(2) Jones believes that the number of planets is divisible by 3.

It is often thought that such failures of substitutivity constitute a positive test orargument that the exchanged expressions do not have the same intension. Thisamounts to an appeal to the principle that cointensive expressions may be freelysubstituted for one another in any syntacticcontext. The principle is plausible because it follows from a principle of compositionfor intensions:

CompositionThe intension of a syntactically complexexpression is a function solely of theintensions of its syntactic parts.

From IDE it follows that (1) and (2) have different intensions; and from this and com-position it follows that the two terms have different intensions. The trouble with com-position, however, is that a strong case canbe made that no two distinct expressionsare freely interchangeable within beliefcontexts. (See Mates, 1950, for the argu-ment.) If so, composition entails that no twoexpressions can have the same intension. Infact, composition has some quite paradoxicalconsequences. From composition it follows

that if expressions u and v of the same syn-tactic type are such that ϕ (u) but not ϕ (v),then u and v do not have the same intension.(Here, ϕ is any sentential context not involv-ing quotation.) But it seems likely that for no predicate F did George IV believe thatnot all Fs are F. (Church (1988) creditsGeorge IV with a healthy respect for thefirst law of identity (that x = x, for all objectsx); and we may assume the same of theprinciple that all Fs are F, for every F.) It nowfollows that if George IV believed that not allFs are Gs, then “F” and “G” have differentintensions. Thus, merely by having certainbeliefs, George IV could control the semanticalfacts about a public language. (This argumentis an ironic analogue of one developed inChurch (1992)). It appears that compositionis too strong (see Putnam, 1954).

If we postulate the converse of IDE – thatexpressions with the same range of extensionshave the same intension – then we have thepoint of view of possible worlds semantics, or more generally of “index semantics”. Theintension of, say, a common noun such as“rose” is identified with the function whichassociates with each sequence of extension-determining factors <p, t, w . . . > (place p,time t, possible world w . . . ) the extension of “rose” with respect to such parameters.This “functional” analysis of intension canbe extended to expressions of complex andhigher type. For example, the relative adjec-tive “small” cannot be treated as a predicateof individuals. The sentence “Dumbo is asmall elephant” does not mean that Dumbois an elephant and Dumbo is small; for if so, we could deduce that Dumbo is a smallanimal from the fact that Dumbo is a smallelephant: “small” combines with a nounphrase (“elephant”) to produce another nounphrase (“small elephant”). Accordingly, the intension of “small” is a function fromcommon noun intensions (functions fromindices to sets) to common noun intensions.This theory has had a considerable impacton research in theoretical linguistics (seeChierchia and McConnell-Genet, 1990).But it is open to many objections, not leastof which is that it makes logical equi-valence the criterion of sameness of inten-sion, though perhaps the most important of

9780631199991_4_P2005.qxd 1/12/09 3:06 PM Page 255

extensionalism

256

which is that it has failed to date to accom-modate certain counterexamples to IDE (see Putnam, 1975).

bibliography

Carnap, R.: Meaning and Necessity (Chicagoand London: University of Chicago Press,1947).

Chierchia, G. and McConnell-Genet, S.:Meaning and Grammar. An Introduction to Semantics (Cambridge, MA: MIT Press,1990).

Church, A.: “A Remark Concerning Quine’sParadox About Modality,” in Propositionsand Attitudes, ed. N. Salmon and S. Soames(Oxford: Oxford University Press, 1988),58–66.

Frege, G.: “On Sense and Reference,” in Trans-lations from the Philosophical Writings ofGottlob Frege, ed. and trans. P. Geach andM. Black (Oxford: Blackwell, 1952), 56–78.

Mates, B.: “Synonymity,” University ofCalifornia Publications in Philosophy 25(1950), 201–26; repr. in Semantics andthe Philosophy of Language, ed. L. Linsky(Urbana, IL: University of Illinois Press,1952), 111–36.

Putnam, H.: “The Meaning of Meaning,” inhis Philosophical Papers II: Mind, Language,and Reality (Cambridge: Cambridge Univer-sity Press, 1975), 215–71.

Putnam, H.: “Synonymity and the Analysisof Belief Sentences,” Analysis 14 (1954),114–22; repr. in Propositions and Attitudes,ed. N. Salmon and S. Soames (Oxford:Oxford University Press, 1988), 149–58.

harry deutsch

extensionalism A theory is said to beextensional if coextensive expressions of thetheory are interchangeable in any syntacticcontext C while preserving the extension ofC. Extensionalism is the doctrine that only(though certainly not all) extensional the-ories are legitimate in the sense of constitut-ing “serious science”. Extensionalism is mostclosely associated with the views of Quine

who goes so far as to claim that formulability

within the framework of extensional predic-ate calculus is “pretty nearly” a necessarycondition of intelligibility (Quine, 1990).

Quine attacks the very notion of meaning(intension), arguing that on close examina-tion this commonplace concept is of no scientific explanatory value; it is a myth, awill o’ the wisp. Quine argues first (but myordering here of Quine’s doctrines is largelyarbitrary) that the concept of meaning as theintensional correlate of individual words andsentences is an obscure notion, subject to no extensional criterion of individuation onand definable only in terms of other, equallyobscure, intensional notions (Quine, 1970).Second, he argues that the traditional ana-lytic/synthetic distinction cannot be main-tained. There is no principled distinctionbetween statements true by definition orlinguistic convention and those true invirtue of extralinguistic fact (Quine, 1951).Third, he observes that incompatible em-pirical hypotheses may each be fully com-patible with the data, and hence insofar as individual hypotheses have “empiricalmeaning”, incompatible hypotheses mayhave the same empirical meaning. Quineinfers from this that empirical significance is diffused over the entirety of theory. Only“observation sentences” have, individually,in isolation from theory, any empirical sig-nificance (Quine, 1970). Fourth, he arguesthat quantified modal logic does not possessan adequate interpretation; at best it en-tails the onerous doctrine of “Aristotelianessentialism” (Quine, 1966 and elsewhere;see essence and essentialism). Finally, heargues that reference is “inscrutable” andtranslation “indeterminate” (Quine, 1960and elsewhere).

The first point is based on a fact of elementary model theory: an isomorphism of one domain onto another leaves thetruth values of sentences undisturbed; andit seems to follow that it simply does notmatter, up to isomorphism, what our termsrefer to. The thesis about translation is theclaim that a theory of translation, that is, atheory about what expressions of the homelanguage translate what expressions of theforeign language, may be underdeterminedby all relevant linguistic data. But, unlike

9780631199991_4_P2005.qxd 1/12/09 3:06 PM Page 256