In the early modern period, poetic form underpinned and influenced scientific progress. The language and imagery of seventeenth-century writers and natural philosophers reveal how the age-old struggle between body and soul led to the brain’s emergence as a curiosity in its own right. Investigating the intersection of the humanities and sciences in the works of authors ranging from William Shakespeare and John Donne to William Harvey, Margaret Cavendish, and Johann Remmelin, Lianne Habinek tells how early modernity came to view the brain not simply as grey matter but as a wealth of other wondrous possibilities – a book in which to read the soul’s writing, a black box to be violently unlocked, a womb to nourish intellectual conception, a creative engine, a subtle knot that traps the soul and thereby makes us human. For seventeenth-century thinkers, she argues, these comparisons were not simply casual metaphors but integral to early ideas about brain function. Demonstrating how the disparate fields of neuroscientific history and literary studies converged, The Subtle Knot tells the story of how the mind came to be identified with the brain.