Slingshot argument

One version of the argument (Perry 1996) proceeds as follows.

Assumptions:

1. Substitution. If two terms designate the same thing, then substituting one for another in a sentence does not change the designation of that sentence.
2. Redistribution. Rearranging the parts of a sentence does not change the designation of that sentence, provided the truth conditions of the sentence do not change.
3. Every sentence is equivalent to a sentence of the form F(a). In other words, every sentence has the same designation as some sentence that attributes a property to something. (For example, "All men are mortal" is equivalent to "The number 1 has the property of being such that all men are mortal".)
4. For any two objects there is a relation that holds uniquely between them. (For example, if the objects in question are denoted by "a" and "b", the relation in question might be R(x, y), which is stipulated to hold just in case x = a and y = b.)

Let S and T be arbitrary true sentences, designating Des(S) and Des(T), respectively. (No assumptions are made about what kinds of things Des(S) and Des(T) are.) It is now shown by a series of designation-preserving transformations that Des(S) = Des(T). Here, "${\displaystyle \iota x}$" can be read as "the x such that".

1.	${\displaystyle S}$
2.	${\displaystyle \phi (a)}$	assumption 3
3.	${\displaystyle a=\iota x(\phi (x)\land x=a)}$	redistribution
4.	${\displaystyle a=\iota x(\pi (x,b)\land x=a)}$	substitution, assumption 4
5.	${\displaystyle \pi (a,b)}$	redistribution
6.	${\displaystyle b=\iota x(\pi (a,x)\land x=b)}$	redistribution
7.	${\displaystyle b=\iota x(\psi (x)\land x=b)}$	substitution, assumption 3
8.	${\displaystyle \psi (b)}$	redistribution
9.	${\displaystyle T}$	assumption 3

Note that (1)-(9) is not a derivation of T from S. Rather, it is a series of (allegedly) designation-preserving transformation steps.

As Gödel (1944) observed, the slingshot argument does not go through if Bertrand Russell's famous account of definite descriptions is assumed. Russell claimed that the proper logical interpretation of a sentence of the form "The F is G" is:

Exactly one thing is F, and that thing is also G.

Or, in the language of first-order logic:

${\displaystyle \exists x(\forall y(F(y)\leftrightarrow y=x)\land G(x))}$

When the sentences above containing ${\displaystyle \iota }$-expressions are expanded out to their proper form, the steps involving substitution are seen to be illegitimate. Consider, for example, the move from (3) to (4). On Russell's account, (3) and (4) are shorthand for:

3'.	${\displaystyle \exists x(\forall y((\phi (y)\land y=a)\leftrightarrow y=x)\land a=x)}$
4'.	${\displaystyle \exists x(\forall y((\pi (y,b)\land y=a)\leftrightarrow y=x)\land a=x)}$

Clearly the substitution principle and assumption 4 do not license the move from (3') to (4'). Thus, one way to look at the slingshot is as simply another argument in favor of Russell's theory of definite descriptions.

If one is not willing to accept Russell's theory, then it seems wise to challenge either substitution or redistribution, which seem to be the other weakest points in the argument. Perry (1996), for example, rejects both of these principles, proposing to replace them with certain weaker, qualified versions that do not allow the slingshot argument to go through. Gaetano Licata (2011) rejected the slingshot argument, showing that the concept of identity (=) employed in Davidson and Gödel's demonstration is very problematic, because Gödel (following Russell) uses the G. W. Leibniz's principle of the identity of indiscernibles, which suffer from the criticism proposed by Ludwig Wittgenstein: to state that x=y when all properties of x are also properties of y is false because y and x are different signs, while to state that x=x when all properties of x are also properties of x is a nonsense. Licata's thesis is that the sign = (usually employed between numbers) needs a logical foundation before being employed between objects and properties.

• Abstraction
• Logic of information
• Charles Sanders Peirce bibliography

• Barwise, K. J. & Perry, John (1981), "Semantic innocence and uncompromising situations", Midwest Studies in the Philosophy of Language, VI.
• Gödel, Kurt (1944), "Russell's mathematical logic", in Paul Arthur Schilpp (ed.), The Philosophy of Bertrand Russell, Evanston and Chicago: Northwestern University Press, pp. 125–53.
• Krüger, Lorenz (1995), "Has the correspondence theory of truth been refuted?", European Journal of Philosophy, vol. 3, 157–173, repr. in Lorenz Krüger, Why Does History Matter to Philosophy and the Sciences?, ed. by Thomas Sturm, Wolfgang Carl, and Lorraine Daston. Berlin: De Gruyter, 2005, pp. 201–217.
• Licata, Gaetano (2011), Truth and Facts: Rejection of the Slingshot Argument in Defence of the Correspondence Theory of Truth, Rome, Aracne.
• Neale, Stephen (1995), "The philosophical significance of Gödel's Slingshot", Mind, vol. 104, no. 416, pp. 761–825.
• Peirce, C. S. (1906), "Prolegomena to an Apology for Pragmaticism", The Monist, 16, 492–546 (1906). Reprinted, Collected Papers, CP 4.530–572. Eprint.
• Perry, John (1996), "Evading the slingshot", in Andy Clark et al. (eds.), Philosophy and Cognitive Science. PDF.

• Stephen Neale's Facing Facts reviewed by John Macfarlane
• An Analysis of Davidson's Slingshot Argument