“Illusion,” then, is wholesome error tending to the ultimate attainment of truth; “delusion” is harmful error arising from a perverted Imagination; “hallucination” is a wandering of the Imagination, without any guidance or support of fact, involving “delusion” of the most obstinate character; “fallacy” is an error of inference or reasoning; “mistake” is the result of mal-observation or weak memory; and “error” a general name for any deviation from the truth. Illusion, in many cases, is an exaggerative and ornative tendency of the mind. It leads the very young to think their parents perfection, and the young to think them far better and wiser than they really are; it constrains the lover to exaggerate the beauty, accomplishments, and qualities of the woman whom he loves; it tends to the distortion of history by inclining all of us to accommodate facts to the wishes and preconceptions of our idealizing nature, which is always longing for “a more ample greatness, a more exact goodness, and a more absolute variety than can be found in the nature of things”;[7] and it lures us onward, young and old alike, over the rough places of life, even to the very brink of the grave, by the ever-fleeting, ever-reappearing suggestions of a bright to-morrow that shall make amends for the dull and commonplace to-day. These illusive hopes, beliefs, and aspirations are never fulfilled in this life; but even the cynic and the pessimist must acknowledge, with Francis Bacon, that they constitute the very basis of all poetry that “tends to magnanimity and morality.” Those who believe in God will further recognize in illusion a divinely utilized integument for the preservation and development of aspirations that shall ultimately find a perfect fulfilment in a harmonious co-operation with the divine Love and in the unending contemplation of the divine Glory. Nor are illusions without a present practical purpose. Men are more hopeful, more active, more loving on account of them. On the other hand, even optimists must acknowledge that no man should shut his eyes to the truth in order to remain in what he knows to be no more than a comfortable error. The venial illusions of childhood, youth, and ignorance, become unpardonable or hypocritical in experienced age. Do you ask how we are to distinguish “illusions” from “delusions”? The answer is easy—on paper; but, in practice, often difficult to apply. However, the test is the same as that by which we distinguish knowledge from ignorance. Illusions “work”; that is to say, men are on the whole the better for them, and they prepare the way for truth. Delusions fail; men are in no way the better for them, and they often prepare the way for insanity and for physical or spiritual death. We have spoken of moral illusions; let us touch on another kind of illusions to which some (I do not say rightly) have given the name of “illusions of sense.”