The terms “realistic” or “naturalistic” art are usually applied to work which is done from the life and hence is true to nature. But their meaning, though definite enough in sculpture, tends to become ambiguous when applied to the graphic arts. If we speak of a naturalistic painting we mean that it is true to the optical impression of the model as observed at a given moment from a given angle. But in a different sense of the term we may speak of naturalism or realism if an artist represents all the details actually in existence, not only those he can see at the moment but those he knows are there as well.
— L. Adam, “Primitive Art”, Pelican Books, 1940.