Ethics is so closely related to psychology--right knowing to right doing--that a brief _hæc fabula docet_ by way of summary may not be out of place. We find, first, a class of sense-deceptions which are due to the nature of our sense-endowment, and deceive only so long as their true character remains unknown. These are neither pernicious nor difficult to correct. Next comes a class of deceptions that deceive because we are ignorant of the possibilities of technical devices, such as those used in legerdemain, and pronounce upon the possibility or impossibility of a certain explanation in advance of complete knowledge. But still another class, and that the most dangerous and insidious, are the deceptions in which self-deception plays the leading rôle. The only safeguard here is a preventive; the thorough infusion of sound habits of thought, a full recognition of the conditions under which the testimony of consciousness becomes dubious, an appreciation of the true value of objective scientific evidence, and an inoculation against the evils of contagion by an independent, unprejudiced, logical schooling. When once the evil spirit of self-deception, fed by the fire of contagion and emotional excitement, begins to spread, reason has little control. As Tyndall tells us, such "victims like to believe, and they do not like to be undeceived. Science is perfectly powerless in the presence of this frame of mind.... It [science] keeps down the weed of superstition, not by logic, but by slowly rendering the mental soil unfit for cultivation." With the spread of an education that fosters independence and self-reliance, with the growth of the capacity to profit by the experiences of others, with the recognition of the technical requisites that alone qualify one for a judgment in this or that field, with a knowledge of the possibilities of deception and of the psychological processes by which error is propagated, the soil upon which superstitions, psychic delusions, mental epidemics, or senseless fads are likely to flourish will gradually be rendered unfit. FOOTNOTES: [3] By Norman Triplett, "The Psychology of Conjuring Deceptions," _American Journal of Psychology_, xi. 4, July, 1900. This most recent and extensive treatment of this topic furnishes a well-selected storehouse of fact, together with suggestive and able interpretations of the material of conjuring deceptions. I shall draw from this material in several portions of this essay, without further detailed acknowledgment.