Definition of Metaphor
Metaphor is a process by which we conceive "one thing in terms of another, and its primary function is understanding" (Lakoff and Johnson, Metaphors We Live By 36). That is, we often do (and must) talk about things that do not physically exist, that we cannot reach out and touch or take apart with our hands to see what is inside and how it works: love, time, anger, life. Sometimes these intangibles are emotions (love, anger); sometimes they are abstractions or names for a whole range of things or activities (argument, friendship). We make them tangible by, in a process of thought, applying models of physical things to them: love is falling; argument is war. This kind of thinking is carried on by us and our culture almost unconsciously -- you would probably not answer someone who asks, "What are you doing?" with, "Oh, nothing, just thinking about argument as war." Where do we see evidence of these thought processes? In our language itself. When someone says, "I defended my position and he backed off," he or she is "thinking" about argument as war whether conscious of it or not. In our Western culture, arguments are typically seen as combative and competitive, but one could imagine cultures in which argument was conceived of as dance. Such a culture would have a different language than ours -- even if it were English!! In that culture, it would be possible to say, "I twirled his idea, then did a dip" -- not only possible to say it, but you would habitually say it (it wouldn't be poetry or some extraordinary or creative use of language) and everyone would know instantly what you mean. It would be a matter of usage -- the way words are typically used in a language and a culture.