Book illustration is supposed to have made a great advance in the last few years. No doubt it has, but this advance has not been made on any definite principle, but, as it were, in and out of a network of cross-purposes. No attempt has been made to classify illustration in relation to the purpose it has to fulfil.
Broadly speaking, this purpose is threefold. It is either utilitarian, or partly utilitarian partly artistic, or purely artistic. The first may be dismissed at once. Such drawings as technical diagrams must be clear and accurate, but by their very nature they are non-artistic, and in regard to art it is a case of "hands off" to the draughtsman.
Illustration as an art, that is, book decoration, begins with the second class. From this standpoint an illustration involves something more than mere drawing. In the first place, the drawing must illustrate the subject, but as the drawing will not be set in a plain mount, but surrounded or bordered by printed type, there is the further problem of the relation of the drawing to the printed type. The relative importance attached to the printed type or the drawing is the crucial point for the illustrator. If all his thoughts are concentrated on his own drawing, one line to him will be much as another; but if he considers his illustration as going with the type to form one homogeneous design, each line becomes a matter of deliberate intention.