Surely when a man is painting a picture he ought not refuse to hear any man's opinion... Since men are able to form a true judgement as to the works of nature, how much more does it behoove us to admit that they are able to judge our faults.

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

The painter strives and competes with nature.

A heightened sense of the observation of nature is one of the chief delights that have come to me through trying to paint. I accumulated in those years so fine a surplus in the Book of Observance that I have been drawing confidently upon it ever since.

The boundaries of bodies are the least of all things. The proposition is proved to be true, because the boundary of a thing is a surface, which is not part of the body contained within that surface; nor is it part of the air surrounding that body, but is the medium interposted between the air and the body, as is proved in its place.

The young man should first learn perspective, then the proportions of objects. Next, copy work after the hand of a good master, to gain the habit of drawing parts of the body well; and then to work from nature, to confirm the lessons learned.