Metaphysics is the philosophical study of reality or being. John Donne is very interested in defining and understanding what is real, and what exists and what does not. One of his more famous poems, "Air and Angels" uses the esoteric difference between the purity of the air, and the purity of angels, who are made of pure spirit (and are therefore more pure than air, according to Donne) to describe the difference between his love for his mistress and her love for him. "As is 'twixt air and angels' purity,/'Twixt women's love and men's will ever be" (531). Though Donne wrote poems with other things in mind than the understanding of the universe, including the racy-for-its-time "Elegy XIX: To His Mistress Going to Bed" (which was refused the license to print in 1633 and not printed until 1669, 523), a large portion of his oeuvre was concerned with making the personal universal. Even short love poems such as "Lovers' Infiniteness" and "A Fever" elevate personal relationships to the heavenly level, with Donne fretting that he cannot have the entirety of his mistress's soul (because it belongs to God) and that if his mistress should die of a fever the world shall be destroyed (527-9). Donne often turns to the otherworldly and the nature of reality, and because of this many of his poems are metaphysical. Source: Holander, John, and Frank Kermode, eds. The Literature of Renaissance England. New York, Oxford University Press, 1973.