The youth should first learn perspective, then the proportions of objects. Then he may copy from some good master, to accustom himself to fine forms. Then from nature, to confirm by practice the rules he has learnt. Then see for a time the works of various masters. Then get the habit of putting his art into practice and work.
[Footnote: The Vatican copy and numerous abridgements all place this chapter at the beginning of the Trattato, and in consequence DUFRESNE and all subsequent editors have done the same. In the Vatican copy however all the general considerations on the relation of painting to the other arts are placed first, as introductory.]
Taken from The Notebooks of Leonardo da Vinci edited by Jean Paul Richter, 1880.