David Kaplan (philosopher)

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David Benjamin Kaplan (born 1933) is an American philosopher and logician teaching at UCLA. His philosophical work focuses on logic, philosophical logic, modality, philosophy of language, metaphysics, and epistemology. He is best known for his work on demonstratives, on propositions, and on reference in opaque (intensional) contexts.

Kaplan received his Ph.D. in philosophy from UCLA in 1964, where he was the last graduate student mentored by Rudolf Carnap. His thesis was entitled "Foundations of Intensional Logic". His work continues the strongly formal approach to philosophy long associated with UCLA (as represented by mathematician-logician-philosophers such as Alonzo Church and Richard Montague).

In most years, Kaplan teaches an upper division course on philosophy of language, focusing on the work of either Gottlob Frege, Bertrand Russell, or P.F. Strawson. His lively lectures often focus on selected paragraphs from Russell's "On Denoting" as well as Frege's "On Sense and Reference."

[edit] Semantics for Indexicals and Demonstratives

Kaplan's most influential contribution to the philosophy of language is his semantic analysis of indexicals and demonstratives, which is outlined (in progressively greater detail) in a series of articles: "Dthat," "On The Logic of Demonstratives," "Demonstratives," and "Afterthoughts".

Kaplan's insights center on two key distinctions, which may be seen as responses to the inability of Frege's semantics to deal with context-sensitivity in language. First, in place of Frege's category of Sinn (Sense: roughly meaning or content), Kaplan introduces the notions of character and content. The former is roughly the meaning of an expression, and the latter is the proposition (or propositional component) expressed by an expression in a context. Second, Kaplan makes an explicit distinction between the context of an utterance and the circumstances of evaluation of the proposition expressed by an utterance. Context can be formalized as a set composed of a speaker, a place, a time, and a possible world (and, depending on the analysis of demonstratives, perhaps a set of either demonstrations or directing intentions). Circumstances of evaluation play a role very similar to possible worlds in modal semantics.

From these rough distinctions, Kaplan then defines character and content more precisely. Character defines a function associated by convention with an expression, which takes contextual elements as arguments and yields content as values. Content, on the other hand, defines a function taking as arguments those elements of the circumstances of evaluation relevant to determining extension, and yielding the extension (referent or truth-value) as a value.

Two more important notions can thus be defined. We can say that an expression is context-sensitive if and only if its character defines a non-constant function (i.e., just in case it yields different content-values given different context-element-arguments). An expression is context-insensitive if and only if its character defines a constant function. Also, the distinction between character and content breaks down in the case of context-insensitive exspressions, and convention associates each such expression directly with a content.

On the other hand, an expression is directly referential just in case its content defines a constant function from circumstances of evaluation to extension. Kaplan also characterizes directly referential expressions as those which refer without the mediation of a Fregean Sinn, or as those whose only contribution to content are their referents. Thus, in the case of directly referential expressions, we can say that the distinction between content and referent breaks down.

Context-sensitive expressions, it turns out, are basically all directly referential according to Kaplan and others (e.g., see John Perry, "Frege on Demonstratives" in The Problem of the Essential Indexical and Other Essays). So the following intuitive picture emerges: the meaning of an indexical is a rule taking us from some part of the context to an extension, and the meaning of a non-indexical is a bit of propositional content which determines the extension in each possible world.

Kaplan goes on to use this semantic scheme to explain phenomena concerning the relationship between necessary and a priori truth. An utterance is said to be necessarily true just in case the content it expresses is true in every possible circumstance; while an utterance is said to be true a priori just in case it expresses, in each context, a content which is true in the circumstances of which that context is a part. So, "I am here now" is true a priori because each of the indexical expressions used ('I', 'here', 'now') directly refer to the speaker, location, and time of utterance. But the utterance is not necessarily true, because any given speaker might have been in at a different place at that time, given different circumstances of evaluation. On the other hand, "I am David Kaplan," as spoken by David Kaplan, is necessarily true, since "I" and "David Kaplan" (both directly referential expressions) refer to the same object in every circumstance of evaluation. The same statement is not true a priori, however, because if it were spoken in a different context (e.g., one with a speaker other than Kaplan), it might be false.

Another result of Kaplan's theory is that it solves Frege's Puzzle for indexicals. Roughly, the puzzle here arises as indexicals are thought to be directly referential, i.e., they do not refer by means of a Fregean Sinn. However, Frege explains cognitive value in terms of Sinn. Thus the following problem emerges: The sentences "I am David Kaplan", spoken by David Kaplan, "he is David Kaplan", spoken by someone pointing at David Kaplan, and "David Kaplan is David Kaplan", spoken by anyone, all express the same content and refer to the same individuals. Yet each of the three has a different cognitive value (it is possible to rationally believe one while denying another). Kaplan explains this by associating cognitive value with character rather than content, thus remedying the problem. (There are problems with this approach, which Kaplan explores in "Afterthoughts".)

Kaplan's semantic theory faces a problem, however, with proper names, which seem both directly referential and context-insensitive. On Kaplan's account, this means that constant functions are defined by both a proper name's character and its content, which would imply that proper names have no meaning other than their reference. While this approach to proper names is not novel (John Stuart Mill being an early advocate), Frege's Puzzle is thought to cast doubt on any such account. Many philosophers have attempted to deal with this issue (notably Scott Soames, Nathan Salmon, Howard Wettstein, Michael Devitt, David Braun, and Joseph Almog), but no solution has been widely accepted.

[edit] Publications

"Quantifying In," Synthese, XIX 1968.
"On the Logic of Demonstratives," Journal of Philosophical Logic, VIII 1978: 81-98; and reprinted in French et. al. (eds.), Contemporary Perspectives in the Philosophy of Language (Minneapolis: University of Minnesota Press, 1979): 401-412.
"Dthat," Syntax and Semantics, vol. 9, ed. P. Cole (New York: Academic Press, 1978); and reprinted in The Philosophy of Language, ed. A. P. Martinich (Oxford: Oxford University Press, 1985).
"Bob and Carol and Ted and Alice," in Approaches to Natural Language (J.Hintikka et. al., eds.), Reidel, 1973.
"How to Russell a Frege-Church," The Journal of Philosophy, LXXII 1975.
"Opacity," in W.V. Quine (L. Hahn, ed.) Open Court, 1986.
"Demonstratives" and "Afterthoughts" in Themes From Kaplan (Almog, et al., eds.), Oxford 1989.
"Words," The Aristotelian Society, Supplementary Volume, LXIV 1990
"A Problem in Possible World Semantics," in Modality, Morality, and Belief (W. Sinnott-Armstrong et al.,eds.) Cambridge, 1995.
"Reading 'On Denoting' on its Centenary", Mind, 114 2005: 934-1003.