s, in other words, a natural symbolism, in which the symbol was
no mere convention, but the actual outward projection of the inner
condition of the mind. Art here offered an equation of inward purpose
and outward expression, neither complete without the other.

Further than this, influenced by Platonic thought, Leonardo's
conception of painting was, as an intellectual state or condition,
outwardly projected. The painter who practised his art without
reasoning of its nature was like a mirror unconsciously reflecting what
was before it. Although without a "manual act" painting could not be
realized, its true problems--problems of light, of colour, pose and
composition, of primitive and derivative shadow--had all to be grasped
by the mind without bodily labour. Beyond this, the scientific
foundation in art came through making it rest upon an accurate
knowledge of nature. Even experience was only a step towards attaining
this. "There is nothing in all nature without its reason," he wrote.
"If you know the reason, you do not need the experience."

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 t