a Muslim” is whether the former individual is a member of the latter set. Different speakers may bring different definitions and denotations to bear on an utterance, and so it is sufficient for some political critics to define the truth condition of “being a Muslim” as membership in the set of people born of at least one Muslim parent, or as membership in the set of people born or raised in predominantly Muslim countries. However one finesses the denotations, “Barack Obama is a Muslim” has different truth conditions than “Barack Obama is a socialist,” as each hinges on membership in different (albeit possibly overlapping) sets, regardless of whether both statements ultimately have the same truth value.
As if defining the literal truth conditions of a predication such as “being a Muslim” or “being a socialist” weren’t hard enough, metaphor poses a further, rather special challenge to the truth-conditional view of meaning. What, for instance, are the truth conditions of the statement “Barack Obama is the Cicero of the 21st Century?” One often needs as much creativity to assign truth conditions to a metaphor as to invent one in the first place. For truth conditions are neither as authoritative or as absolute as they seem, nor are they designed by experts to be shared by all. Rather, truth conditions are often speaker-relative and context-sensitive. One speaker may think that to truthfully call one a socialist, it is enough that this person openly espouse socialist values. Another may think it sufficient for one to act like a socialist, whether one actually thinks of oneself as a socialist or not. These speakers are likely to disagree over the truth conditions of the statement “Barack Obama is a socialist,” yet this is not a problem for metaphor or for language. The truth conditions of a metaphor often arise from a tacit negotiation between speaker and hearer of the meaning of the metaphor, rather than the other way around.
Philosophers who are otherwise bullish about truth conditional semantics are often bearish toward the idea in the context of metaphor. Donald Davidson, for instance, questions the usefulness of truth conditions for arriving at the meaning of a metaphor. For Davidson [1978], a metaphor does not so much communicate a meaning as inspire a meaning, leading him to argue that “the attempt to give literal expression to the content of the metaphor is simply misguided.” Thus, in the metaphor “my car drinks gasoline,” only some of the truth conditions associated with literal uses of the verb to drink will be applicable in the metaphorical context of a drinking car, but none of these carry the weight of the interpretation that the speaker hopes to inspire in the listener (for instance, that my car requires too much gasoline to operate). These truth conditions include, for instance, the expectation that the drinker is an animate creature, that the substance consumed is a potable liquid, and that the drinker both consumes the liquid and derives some chemical benefit from it. Just two of these truth conditions are sensible for the metaphor “my car drinks gasoline,” namely that my car consumes gasoline and derives some chemical value from it. In effect, this is the truth-conditional equivalent of Aristotle’s strategy (b), whereby the species to drink is displaced onto its genus to consume. However, to suggest that this banal observation is the speaker’s intended meaning is to fly in the face of Grice’s maxim of informativeness (see Grice [1978]), since the claim of gasoline consumption holds for most cars and is hardly worth mentioning in the context of this car. Rather, as we can expect most listeners to know that cars consume gasoline, that people generally only drink what they want to drink (and thus drink what they like), then the speaker’s most likely meaning is my car likes to drink gasoline and thus consumes a lot of gasoline, rather more than I would prefer. This meaning cannot be derived from the truth-conditional semantics of the words in the metaphor, but can only emerge from a pragmatic understanding of the world knowledge behind the words.
Black [1962] proposes an interactionist view of metaphor that explains how the meaning of a metaphor emerges from a heuristic, common-sense consideration of possible interactions between the ideas raised by the metaphor. For Black, the meaning of a metaphor is more than the sum of the meaning of its parts, and a surprising meaning may thus emerge from the juxtaposition of two rather familiar ideas (in this sense, Black foreshadows the notion of emergent meaning developed by Fauconnier and Turner [2002] in the context of their theory of conceptual blending). The use of common-sense knowledge—such as cultural associations, folk beliefs, conventional implicatures, and so on—offers a much richer and open-ended basis for exploring the associations and beliefs that emerge in the mind of the listener in response to a metaphor than a purely truth-conditional approach based on denotations and set membership. As in the more contemporary take on Black’s interaction view of metaphor offered by Indurkhya [1992], metaphor is not so much a user of pre-existing similarity as a creator of new similarities, insofar as the meaning that emerges from a metaphorical juxtaposition reveals the source and target to be more similar than the listener may have previously realized. Davidson and Black (and later researchers such as Indurkhya) agree that what makes metaphor special is not the truth conditions imposed by its words on the semantics of the specific utterance, but the system of ideas and associations that are evoked—in response to the metaphor—in the mind of a “suitable” listener in a “suitable” context. A key question for Davidson is whether this system of ideas and associations can be considered the secondary or special meaning of the metaphor (where the literal interpretation serves as the primary meaning), or indeed whether it is well-founded to consider a metaphor as having such a secondary meaning. As Davidson [1978] points out, similes do their work without the need for a secondary meaning—they typically mean what they purport to mean on the surface—so why should metaphors be any different?
Specifically, Black and Davidson disagree on the extent to which it is sensible to speak of the special meaning of a metaphor (as opposed to the literal meaning that resides on the surface) as a parcel of cognitive content that is communicated from speaker to listener. Davidson [1978] explicitly denies the position (which he attributes to Black) that a metaphor “asserts or implies certain complex things by dint of a special meaning and thus accomplishes its job of yielding an insight” (his italics). For Davidson, to speak of the meaning of a metaphor as a distinct message or insight is simply wrong-headed, as misguided as speaking about the definitive meaning of a poem, a joke, or a theatrical play. For instance, what does it mean to speak of the meaning of a play? At one level, the only level at which Davidson argues that it is sensible to speak of the meaning of a metaphor, a play means just what its words and sentences purport to mean, although it may also nudge a viewer to think certain thoughts or consider certain possibilities about the world. The deeper meaning of a play, what one might call its message to the audience, is not contained in the text itself, but is inspired in the mind of a viewer. Davidson’s view is reminiscent of the angry response by the Irish playwright Brendan Behan to an interviewer who had asked him to summarize the message of his most recent work: “Message? What the hell do you think I am, a postman?” However, the fact that two viewers may find themselves in agreement in their responses to a play, and find that their responses agree with those intended by the playwright, suggests that playwrights may nonetheless be successfully asserting some secondary meaning via their work. Likewise, the fact that listeners may agree as to the insights delivered by a metaphor, and agree with the speaker as to the nature of these insights, speaks to the reality that speakers often do aim to assert something with their metaphors that is not to be found in the literal meaning of their statements. Indeed, as Black [1979] notes, the fact that listeners may disagree with each other, or with a speaker, in their response to a metaphor suggests that speakers do wish to assert some measure of propositional content with their metaphors. The difficulty of precisely pinpointing and circumscribing this propositional content (or the impossibility of doing this in principle for all metaphors) should not lead us to infer that it never exists, or give up on the task of trying to pinpoint (formally or computationally) at least part of this meaning.
2.3 PARAPHRASING METAPHOR
Most discussions about the meaning of a given metaphor inevitably turn on our ability to produce a convincing paraphrase. Yet Davidson [1978] raises a cautionary note when he argues that “what we attempt in ‘paraphrasing’ a metaphor cannot be to give its meaning, as that lies on the surface; rather, we attempt to evoke what the metaphor brings to our attention.” So just what is a paraphrase then? If we take what “lies on the surface” of a metaphor