An indirect comparison of two unlike things in which some quality of one is transferred to the other
He even imagined that his music could reach into people’s hearts and melt away their sadness.
In the underlined portion, sadness is indirectly compared to a solid that can melt. The purpose may be to give substance to sadness and to make it seem hard and cold like ice, so that Mole’s music is characterized as powerful and warm.
But soft, what light through yonder window breaks?
It is the east, and Juliet is the sun.
In the underlined portion, Juliet’s window is compared to the east, where the sun rises, and Juliet is compared to the sun. The purpose of the comparison might be to say that Juliet is beautiful, important, and warm…It transfers the positive associations of the sun to Juliet.
All forms of metaphor and simile are examples of analogy, a broader term for any explanatory comparison.
The origins of the word “metaphor,” from Greek, translate to something like “to transfer.” That is useful, because a metaphor consists of transferring the qualities of one thing, often referred to as “the vehicle,” to some other thing, often referred to as “the tenor.” The purpose of the transfer is to communicate some idea about the tenor. This transfer is often described as a comparison, but the comparison is indirect.
Source: Metaphor. http://en.wikipedia.org/wiki/Metaphor. Accessed October 9, 2012.