This paper examines the question of error in perspective from the viewpoint of the painter, notthe spectator. This distinction significantly modifies the way in which perspective is approached for one must view it with the eye of the painter or the architect who constructed it. The perspective is therefore judged interms of the methods used by its creator, which is to say in terms of the goals he set himself and the means at his disposal in order to achieve them. We then explain the "good reasons" the Renaissance painters had to consent to the three main types of error in perspective: "accidental errors" (type I), "ad hoc errors" (type II) and "systematic errors" (type III).