For Leonardo painting is supreme among the sciences, since it is based on the mathematical principles of perspective, it recurs to the verification of experience and is nourished by universal knowledge. The fundamental instrument for the painter is the eye, directly connected to the mind, and thus to the soul.

The "science of painting" consists of the process which, through the eyes, passes from nature to the mind and, by means of the hands, from the mind to the painting. Painting is "mental discourse", capable of imitating to perfection all of the natural forms and of endlessly inventing other forms.