To teach how to foreshorten, entirely as a separate proposition, is difficult. Definitions of the word itself are somewhat vague. "Foreshorten to represent figures as they appear to the eye when seen obliquely"; "to represent objects in accordance with the laws of perspective"; "the art of diminishing the entire length of an object when viewed obliquely."
"Foreshortening is to draw what we don't see," explained an exasperated art student on being examined as to his knowledge of certain rules of drawing. One can sympathize with him if not agree with his definition.
Knowledge of the rudiments of perspective gives one a. better conception of the proper manner to foreshorten an object, animate or otherwise, than any amount of special instruction on the subject. Foreshortening is one branch of the study of the elementary laws of perspective.
Much of what we see in nature is foreshortened. With the exception of the lines at right angles with the line of vision, all dimensions appear foreshortened. Unless one were looking through a hole in the ceiling, the table and practically every article in a room would appear foreshortened.
Even the pictures on the wall, if above the level of the eye, are seen foreshortened. This will not be the case if they are tilted in such a way that their surfaces are at right angles to the line of vision.
The pupil may be able to draw in perspective, according to instruction, a hemisphere and a cylinder lying on their sides and yet not realize that the same instruction applied to any object offering a round plane surface, as its principal problem for the moment, is of equal value a lemon for instance.
Having drawn a hemisphere, a cylinder and a lemon, the same pupil may ask, "How do you draw the two wheels of a cart?" The answer is: By the same rules as one draws the two planes of a cylinder lying on its side.
The pupil, having mastered these, comes back inquiring how to foreshorten a leaf.