As we want to write these very brief commentaries on painting, we will first take from mathematicians things that will seem to pertain to the subject so as to make our presentation clearer. Having known, without doubt, these things, we will explain the art of painting, as long as talent will not fail, beginning from Nature's principles themselves.(1) But in every expression of ours, I ask earnestly to bear in mind that I speak of these things not as a mathematician but as a painter. Those [the mathematicians], in fact, measure figures and shapes of things with the mind only, without considering the materiality of the object. We [painters], instead, since we want an object to be visible, in writing we shall express [ourselves] through good common sense, as one says.(2) Furthermore, we believe we have reached our purpose if the painters who read us will be able to understand this matter, clearly difficult, and treated by nobody else, as far as I know, by means of written documents in whatever way. (3) I then ask that they [the painters] consider our commentaries as written, not by a pure mathematician but only as by a painter.