Conceit

In literature, a conceit is an extended metaphor with a complex logic that governs a poetic passage or entire poem. By juxtaposing, and manipulating images and ideas in surprising ways, a conceit invites the reader into a more sophisticated understanding of an object of comparison. Extended conceits in English are part of the poetic idiom of Mannerism, during the late sixteenth and early seventeenth century.

In English literature the term is generally associated with the 17th century metaphysical poets, an extension of contemporary usage. The metaphysical conceit differs from an extended analogy in the sense that it does not have a clear-cut relationship between the things being compared.Helen Gardner observed that "a conceit is a comparison whose ingenuity is more striking than its justness" and that "a comparison becomes a conceit when we are made to concede likeness while being strongly conscious of unlikeness." An example of the latter occurs in John Donne's "A Valediction: Forbidding Mourning", in which a couple faced with absence from each other is likened to a compass.

Dull sublunary lovers' love
   (Whose soul is sense) cannot admit
Absence, because it doth remove
   Those things which elemented it.

But we by a love so much refined,
   That our selves know not what it is,
Inter-assured of the mind,
   Care less, eyes, lips, and hands to miss.

Our two souls therefore, which are one,
   Though I must go, endure not yet
A breach, but an expansion,
   Like gold to airy thinness beat.

If they be two, they are two so
   As stiff twin compasses are two;
Thy soul, the fixed foot, makes no show
   To move, but doth, if the other do.

And though it in the center sit,
   Yet when the other far doth roam,
It leans and hearkens after it,
   And grows erect, as that comes home.

Such wilt thou be to me, who must,
   Like th' other foot, obliquely run;
Thy firmness makes my circle just,
   And makes me end where I begun.

The metaphysical conceit is often imaginative, exploring specific parts of an experience.John Donne's "" is a poem seemingly about fleas in a bed. When Sir Philip Sidney begins a sonnet with the conventional idiomatic expression "My true-love hath my heart and I have his". He takes the metaphor literally and teases out a number of literal possibilities in the exchange of hearts. The result is a fully formed conceit.

...
Wikipedia