Metaphysical conceits are expansive metaphors marked by paradox, wit, symbolism, double meanings, analytical tone, and logical reasoning. However, the complexity and form of metaphysical conceits is difficult to understand just by description. John Donne, who is considered the first metaphysical poet, created text book example of a metaphysical conceit in the second half of "A Valediction: Forbidding Mourning" :
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 th' 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.
Donne wrote this famous conceit comparing two departed lovers to a compass. By compass, he means a drawing compass- one that makes geometric circles, not the kind of compass that points to the magnetic poles. Through the strange, but fitting comparison, he tries to capture the idea that as one lover, or compass leg, moves further away, the one remaining stationary will "lean and hearken" after it. The idea of a circle is important, too. Circles have all sorts of symbolic meanings: eternity, completeness, and perfection to name a few. Comparison between unlikely and dissimilar things is a common feature of these figures of speech. The final line about growing erect as it comes homes has fairly obvious double meanings.
However, this example lacks the use of paradoxes found in many other metaphysical conceits. Once again, Donne's poetry shows an outstanding example in "Batter my heart, three person'd God":
Batter my heart, three-person'd God, for you
As yet but knock, breathe, shine, and seek to mend;
That I may rise and stand, o'erthrow me, and bend
Your force to break, blow, burn, and make me new.
I, like an usurp'd town to'another due,
Labor to admit you, but oh, to no end;
Reason, your viceroy in me, me should defend,
But is captiv'd, and proves weak or untrue.
Yet dearly I love you, and would be lov'd fain,
But am betroth'd unto your enemy;
Divorce me, untie or break that knot again,
Take me to you, imprison me, for I,
Except you enthrall me, never shall be free,
Nor ever chaste, except you ravish me.
The entire poem is both a metaphysical conceit and paradoxical; Donne is asking God for spiritual salvation and destruction simultaneously. Even in the later part where the overtone is love and marriage (contrasting to the bending, breaking and burning through the first part), he asks for "divorce" and to "break that knot again".
Through highly irregular comparisons that seemingly have nothing in common, metaphysical conceits are able to paint an exact emotion or idea. The metaphysical poets of the 17th century are often associated as the primary users of these. Rarely have any other poets or groups of poets explored this type of conceit.
Source: Murfin, Ross. The Bedford Glossary of Critical and Literary Terms. Boston, MA: Bedford, 1998.