In the history of art, as well, he urged that nature had been the test of its excellence. A {xvi} natural phenomenon had brought art into existence. The first picture in the world, he remarked in a happy epigram, had been "a line surrounding the shadow of a man, cast by the sun on the wall." He traced the history of painting in Italy during its stagnation after the decay of ancient art, when each painter copied only his predecessor, which lasted until Giotto, born among barren mountains, drew the movements of the goats he tended, and thus advanced farther than all the earlier masters. But his successors only copied him, and painting sank again until Masaccio once more took nature as his guide. A quite different and combative side to Leonardo's aesthetic, which forced him to state the broad principles of art, appears in his attacks on poetry and music as inferior to painting. In that age of humanistic triumph, literature had lorded it over the other arts in a manner not free from arrogance. There was still another cause for his onslaught on poetry. Leonardo resented the fact that painters, who were rarely men of education, had not defended themselves against the slurs cast on their art. His counter attack may have been intended to hide his own small scholarship. It served another end as well. His conception of the universal principles of beauty was made clear by this defence. His first principle stated broadly that the most useful art was the one which could most easily be communicated. {xvii} Painting was communicable to all since its appeal was made to the eye. While the painter proceeded at once to the imitation of nature, the poet's instruments were words which varied in every land. He took the Platonic view of poetry as a lying imitation, removed from truth. He called the poet a collector of other men's wares, who decked himself in their plumage. Where poetry presented only a shadow to the imagination, painting offered a real image to the eye; and the eye, as the window of the soul through which all earthly beauty was revealed, the sight, he exclaimed, which had discovered navigation, which had impelled men to seek the West, was the noblest of all the senses. Painting spoke only by what it accomplished, poetry ended in the very words with which it sang its own praises. If, then, poets called painting dumb poetry, he could retort by dubbing poetry blind painting. In common with his successors, Leonardo could not escape from this fallacy, which, in overlooking all save descriptive verse, was destined to burden aesthetic until demolished by Lessing.