Metaphor, the description of one thing as something else, has become of interest in recent decades to both analytic philosophy and continental philosophy, but for different reasons.
Metaphor in analytic philosophy
In the Anglo-American tradition of analytic philosophy (in particular, in the philosophy of language), metaphor has attracted interest because it does not conform to accepted truth-conditional semantics, the conditions which determine whether or not a statement is true. Taken literally, the statement "Juliet is the sun" (from Romeo and Juliet) is false, if not nonsensical, yet, taken metaphorically, it is meaningful and may be true, but in a sense which is far from clear. The comparison theory of metaphor asserts that one can express the truth value of a metaphor by listing all the respects in which the two terms are alike or similar; for example: Juliet is like the sun because she shares with it qualities such as radiance, brilliance, the fact that she makes the day and that she gets up every morning. However, this results in re-casting metaphor as simile. Because it can only explain the truth of metaphor by in effect losing metaphor, the comparison theory is rarely defended.
In contrast, two leading theorists emphasize the fact that truth conditions cannot be specified for a metaphor. Max Black maintains that metaphors are too open-ended to be able to function as referring expressions, and so cannot be expressions which have truth conditions . If metaphors are used in contexts where precise terminology is expected (for example, in a scientific theory), then their role, Black argues, is purely heuristic, that is, they are means to an end or ways of assisting understanding, rather than being terms which can be tested for truth or falsity . Donald Davidson also thinks it a mistake to look for the truth conditions of a metaphor, since, in his words, "much of what we are caused to notice [in a metaphor] is not propositional in character", that is to say, metaphor is a prompt to thought which cannot be reduced to or contained by a series of truth conditions . What metaphor does, Davidson maintains, is make us see one thing as something else by "making [a] literal statement that inspires or prompts the insight" . Seeing one thing as something else is not the recognition of some truth or fact, and so "the attempt to give literal expression to the content of the metaphor is simply misguided" .
Max Black develops the idea that metaphor actually creates insight or new meaning . His interactionist theory asserts that at the heart of a metaphor is the interaction between its two subject terms, where the interaction provides the condition for a meaning which neither of the subject terms possesses independently of the metaphorical context. The primary subject in a metaphor, he claims, is coloured by a set of "associated implications" normally predicated of the secondary subject . From the number of possible meanings which could result, the primary subject sieves the qualities predicable of the secondary subject, letting through only those that fit. The interaction, as a process, brings into being what Black terms an "implication-complex", a system of associated implications shared by the linguistic community as well as an impulse of free meaning, free in that it is meaning which was unavailable prior to the metaphor's introduction .
In a different, naturalist, approach, some English-speaking philosophers close to cognitive science, such as Lakoff, have made metaphor the central aspect of human rationality.
Metaphor in continental philosophy
Whereas analytic philosophy examines metaphor within the philosophy of language, continental philosophy assigns much wider significance to metaphor. This is because the climate within continental thought has been more favourable to the propagation of new branches of enquiry from nineteenth century German philosophy. Although Kant and Hegel sit quite happily on both analytic and continental curricula, it is only the latter which has seriously addressed the need to rethink how the world appears to us and how it is made manifest to us in the light of their metaphysics. Metaphor has proven to be extremely important for this rethinking because it is the process of conceptual borrowing or reassignment which revises our perception of the world.