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According to Aristotle, a metaphor involves taking something appropriate to one class of things and applying it to something alien.
This view of a metaphor as a challenging juxtaposition of ideas is somewhat akin to paradox, (meaning in Greek "contrary to expectation", or more colourfully, "beyond belief") and relates well to the experience of enjoyment in tackling the obvious mistakenness of a paradox, and the satisfaction of a resolution. Paradoxes motivate us to think intensely, and critically examine our existing knowledge, in an effort to incorporate something new and unexpected.
In "Essay on what I think about most", the poet and classicist Anne Carson reflects that metaphor teaches us:
Not only that things are other than they seem,
and so we mistake them,
but that such mistakenness is valuable.
Hold onto it, Aristotle says,
there is much to be seen and felt here.
Metaphors teach the mind
to enjoy error
and to learn