The metaphysical poets (17th century, British), who were not all aware of each other or aware of forming a metaphysical school, all shared certain characteristics as a result of the changes in science and society which reflected the way they looked at the world. The metaphysical poets used metaphors and metaphysical conceit (elaborate, extended metaphor of specialized kind, even when talking about natural or earthly things. Thus, they wrote poetry on earthly things but in abstract or other than physical (meta means above) terms, often with spiritual themes. Also they would write on souls, spirits, ideals and abstracts, such as love, and their relation to the physical world.
It may be that Descartes had an influence on these poets since they were all contemporaries. But he was a mathematician and philosopher who coined “I think therefore I am,” which created the concept of a ghost in the machine (a Soul in the body). There may have been a general historically collective consciousness about the differences between soul and body, mental and physical, during this period, which was the end of the Renaissance, an era known, paradoxically, for intellectual advances and nostalgia for the Classical Age.
George Herbert was a metaphysical poet who wrote all of his poems with a religious theme. Religion = spiritual = metaphysical (above physical or non-physical).
John Donne is the most famous metaphysical poet. He wrote on spiritual themes but also often linked them with sex and love. Perhaps this was most famously done in “The Flea,” which is an extended metaphor (conceit) of those themes. In “The Canonization” Donne describes love as a canonized Saint, as being earthly-immortal and spiritually immortal.
Katherine Phillips is sometimes called a metaphysical poet. She wrote of the superiority of social or mental love over physical love. She presents a contrast to Donne’s celebration of the physical and metaphysical. However, her praise of mental over physical could also be interpreted not as scorn for physical love but scorn for the way physical love was portrayed and/or its traditional or patriarchal tendencies.
Then let our flames still light and shine,
And no false fear control,
As innocent as our design,
Immortal as our soul.
(“To My Excellent Lucasia on our Friendship”)
Milton and Spenser are not considered metaphysical poets although they do use metaphysical themes. The metaphysical poets were a specific group at a specific time.