When thought, action, or animation is implied, it is generally demanded that the head be tipped. Note that the head is tipped in Figure 10 (Windblown), although the angle is full-face. The animation of the expression, the swing of the hair, all require that the head be tipped. If this picture is framed with the features vertical, it immediately becomes stiff and uncomfortable, and at the same time loses a certain feminine delicacy.

William Mortensen, The Model: A Book on the Problems of Posing (1937), p. 30