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Reduction and Elimination in Philosophy and the Sciences

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116<br />

Deflationism <strong>and</strong> Conservativity: Who did Change <strong>the</strong> Subject? — Henri Gal<strong>in</strong>on<br />

<strong>the</strong>ory, that is arithmetic <strong>in</strong> <strong>the</strong> case <strong>in</strong> po<strong>in</strong>t, that<br />

claim can only be susta<strong>in</strong>ed by an argument to <strong>the</strong><br />

effect that our meta<strong>the</strong>ory is sound as an<br />

arithmetical <strong>the</strong>ory: for <strong>in</strong> general, it is just not true<br />

that <strong>the</strong> restriction of <strong>the</strong> truth <strong>the</strong>ory of a <strong>the</strong>ory A to<br />

<strong>the</strong> vocabulary of A is sound for <strong>the</strong> <strong>in</strong>tended model<br />

of A! (remember it was not sound as an arithmutical<br />

<strong>the</strong>ory). But how do we know that our meta<strong>the</strong>ory is<br />

arithmetically sound? There's noth<strong>in</strong>g <strong>in</strong> our base<br />

<strong>the</strong>ory that can guarantee this. Clearly our<br />

recognition of T(PA) as arithmetically sound<br />

amounts to our acknowledgement of some systems<br />

stronger than PA as be<strong>in</strong>g arithmetical systems<br />

(T(PA) with unduction on unrestricted vocabulary, or<br />

second-order arithmetic <strong>in</strong> <strong>the</strong> case of an explicitely<br />

def<strong>in</strong>ed truth-predicate, etc.). In o<strong>the</strong>r words, a claim<br />

that T(PA) is non-conservative over PA <strong>and</strong><br />

arithmetically sound amounts to a bold statement of<br />

new axioms for arithmetic above PA. It is not our<br />

commitment to truth which is do<strong>in</strong>g <strong>the</strong> relevant nonconservative<br />

job, but our commitment to PA be<strong>in</strong>g<br />

arithmetic <strong>and</strong> to T(PA) be<strong>in</strong>g a stronger,<br />

arithmetically sound, <strong>the</strong>ory.<br />

3. The Moral<br />

The moral of this story is simple. If someone knows that<br />

PA is true, he can conclude that PA is consistent. But he<br />

won't be able to convert this <strong>in</strong>to arithmetical knowledge,<br />

that is to derive any new arithmetical fact, unless his arithmetical<br />

knowledge outreaches PA from <strong>the</strong> start. And it<br />

seems <strong>in</strong>evitable <strong>the</strong>n to say that it is this hidden knowledge,<br />

which is unfolded <strong>in</strong> <strong>the</strong> course of build<strong>in</strong>g <strong>the</strong> truth<strong>the</strong>ory,<br />

that does <strong>the</strong> explanatory work. More generally,<br />

knowledge that an <strong>in</strong>terpreted <strong>the</strong>ory A is true yields<br />

knowledge that A is consistent. But it will never <strong>in</strong> itself<br />

give any new <strong>in</strong>sights <strong>in</strong>to A-facts, unless one knew from<br />

<strong>the</strong> beg<strong>in</strong>n<strong>in</strong>g that A was somehow expressively defective<br />

relative to his actual knowledge concern<strong>in</strong>g <strong>the</strong> <strong>in</strong>tended<br />

field of T <strong>and</strong> had some ways to recognize some extensions<br />

of T as be<strong>in</strong>g sound relative to his knowledge of Tfacts.<br />

Were this last condition not met, how could he be<br />

sure that one did not change <strong>the</strong> subject?<br />

It seems fair to conclude that <strong>the</strong> conservativity argument<br />

does not show that truth has any explanatory power by<br />

itself. On <strong>the</strong> contrary, close <strong>in</strong>spection of <strong>the</strong> argument<br />

tells <strong>in</strong> favor of <strong>the</strong> <strong>the</strong>sis that "true" is a genu<strong>in</strong>e<br />

expressive device.<br />

Literature<br />

Field, Hartry. 1999 "Deflat<strong>in</strong>g <strong>the</strong> conservativness argument",<br />

Journal of <strong>Philosophy</strong> 96, 533–540.<br />

Ketl<strong>and</strong>, Jeffrey, 1999 "Deflationism <strong>and</strong> Tarski’s paradise". M<strong>in</strong>d<br />

108, 69–94.<br />

McGee,Van 1991 Truth, Vagueness <strong>and</strong> Paradox. Indianalpolis:<br />

Hackett.<br />

Shapiro, Stewart 1998 "Proof <strong>and</strong> truth: Through thick <strong>and</strong> th<strong>in</strong>",<br />

Journal of <strong>Philosophy</strong> 95, 493–521.

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