A painter should begin every canvas with a wash of black, because all things in nature are dark except where exposed by the light.

I abhor the supreme folly of those who blame the disciples of nature in defiance of those masters who were themselves her pupils

Just as iron rusts from disuse, and stagnant water putrefies, or when cold turns to ice, so our intellect wastes unless it is kept in use.

Those who fall in love with practice without science are like a sailor who enters a ship without a helm or a compass, and who never can be certain whither he is going.

Especially learn how to see.

Being willing is not enough. We must do.

The limiting surface of one thing is the beginning of another.