The poems of Leaves of Grass are loosely connected, with each representing Whitman's celebration of his philosophy of life and humanity. This book is notable for its discussion of delight in sensual pleasures during a time when such candid displays were considered immoral. Where much previous poetry, especially English, relied on symbolism, allegory, and meditation on the religious and spiritual, Leaves of Grass (particularly the first edition) exalted the body and the material world. Influenced by Ralph Waldo Emerson and the Transcendentalist movement, itself an offshoot of Romanticism, Whitman's poetry praises nature and the individual human's role in it. However, much like Emerson, Whitman does not diminish the role of the mind or the spirit; rather, he elevates the human form and the human mind, deeming both worthy of poetic praise. Leaves of Grass was highly controversial during its time for its explicit sexual imagery, and Whitman was subject to derision by many contemporary critics. Over time, the collection has infiltrated popular culture and been recognized as one of the central works of American poetry.