"To be a master of metaphor," Aristotle wrote in his Poetics, "is the greatest thing by far. It is the one thing that cannot be learnt from others, and it is also a sign of genius." He described it most simply as "giving the thing a name that belongs to something else." More recent thinkers explain its analytic structure with greater precision. One locus classicus is the philosopher Max Black's 1955 article, ''Metaphor,'' in which he set forth three traditional views of the device that still guide debate about it.
The ''substitution'' theory argues that a metaphor of the form ''A is B'' (Shakespeare's ''Juliet is the sun") presents some intended literal meaning of the form ''A is C'' (''Juliet is the center of my solar system"). The ''comparison'' theory, probably the most widely held, interprets the ''A is B'' metaphor as an elliptical simile that really asserts ''A is like B in the following respects. ... '' Here, the reader or listener must ferret out the relevant respects. ''Juliet is the sun'' may call attention to Juliet's gravitational influence on Romeo, the heat she radiates, the light she emits, or all these characteristics and more. Last, the ''interaction'' theory suggests that the ''system of associated commonplaces'' of A and B somehow merge to create a distinct metaphorical meaning that no literal statement captures. {Read on via Chronicle.com}