There has been no man of pure Genius; as there has been none wholly destitute of Genius.
 Henry David Thoreau, A Week on the Concord and Merrimack Rivers (1849). copy citation

Context

“The Man of Genius, referred to mankind, is an originator, an inspired or demonic man, who produces a perfect work in obedience to laws yet unexplored. The Artist is he who detects and applies the law from observation of the works of Genius, whether of man or nature. The Artisan is he who merely applies the rules which others have detected. There has been no man of pure Genius; as there has been none wholly destitute of Genius. Poetry is the mysticism of mankind. The expressions of the poet cannot be analyzed; his sentence is one word, whose syllables are words. There are indeed no words quite worthy to be set to his music.” source