 According to Hyman, this principle captures an exact relationship between the marks on a picture’s surface and the picture’s sense, which does not depend on the artist’s intention, or on the picture’s psychological effect on a spectator, and which applies to pictures regardless of their style or the artistic tradition to which they belong. Together with a principle concerning colour, it is supposed to explain how the colours and shapes on the surface of a picture fix the colours and shapes of the objects it depicts. But Hyman’s optical principles do not imply that a portrait of Tolstoy resembles Tolstoy, since they are only concerned with a picture’s sense, as opposed to its reference. Nor do they imply that a painting of a bearded man resembles a bearded man, since they are only concerned with the shapes and colours of the objects in a picture. Hyman therefore claims that his theory dovetails neatly with the idea that a picture’s reference is normally determined by the artist’s intention, and with the idea that the depiction of objects of specific kinds, such as men and horses, depends on a picture’s propensity to trigger a spectator’s ability to recognize these kinds of objects by their shapes and colours, and the shapes and colours of their parts (see below,  §3.2).  He explains how these two elements of a theory of depiction can be combined with the example of a silhouette: