It was a motto of Jesus that “As a man thinketh in his heart, so is he.” Although the particular phrase, “in his heart,” is now regarded as too wild a hyperbole to be justified by the facts, yet the all-or-none principle furnishes an unsuspected substantiation of the essential truth of this motto with respect to certain individuals. We have long known that thinking did somehow lead to action,—that both the rogue and the philanthropist, the slanderer and the coquette often schemed and planned secretly for years without giving any outward hint of what their future behavior was to be. History is full of the trouble caused for those who had “no art to read the mind’s construction in the face” of him who could “smile and smile and be a villain.” And now the secret is out why for so many centuries it was believed that thought produced action and mind ruled matter. Thought _is_ action, but action of so elusive a character as to be totally beyond the unaided eye to detect; and thought “leads” to action for the same reason that a spark can produce a conflagration and a hole in a dyke produce a flood. In all three cases the greater effect is due to the magnification of the exciting cause. The ancients held that mind ruled the body for the reason that, being ignorant of the fact of covert muscular responses, they assumed an incorporeal cause for a series of events whose end-term alone they were able to discern as embodied in the movements of matter. It is thus finally apparent how by means of the law of the conditioned reflex and the all-or-none principle, both concrete and abstract terms serve not only as gestural signs, but also serve to imply and predict human activities. We have shown that every word which has a meaning _ipso facto_ implies action. It matters not whether that action be sudden or violent, or merely one that is carried out on “low gear,” so to speak, by the neuro-muscular mechanisms of the body. Neither does it matter whether that action be precise or groping, specific or diffuse; if the word has a meaning it will be accompanied by an action-tendency, and that tendency will be added to the kinetic potentialities,—the character,—of the individual. For if it is the case that by the law of the conditioned reflex, words _get_ meaning, it is equally to be asserted that by virtue of the all-or-none principle, they _keep_ it. Moreover, Holt to the contrary notwithstanding, it is such demonstrable physiological principles as these, and not the mysterious Freudian categories, which are the keys whereby the secrets of mind will be unlocked.