among the "common sensibles," there is a certain resemblance between Aristotle’s doctrine and Kant’s theory that recognition of spatial and temporal order is a function not of understanding but of "pure" sense. It is further held that to be aware that one is perceiving (self-consciousness) and to discriminate between the different classes of "special" sense-perception must also be functions of the "common sense-organ." Thus Aristotle makes the mistake of treating the most fundamental acts of intelligent reflection as precisely on a par, from the point of view of the theory of knowledge, with awareness of colour or sound. A more legitimate function assigned to the "common sensorium" in the heart is that "fantasy," the formation of mental imagery, depends on its activity. The simplest kind of "image," the pure memory-image left behind after the object directly arousing perception has ceased to stimulate, is due to the persistence of the movements set up in the heart after the sensory process in the peripheral organ is over. Since Aristotle denies the possibility of thinking without the aid of memory-images, this function of the "common sensorium" is the indispensable basis of mental recall, anticipation, and thought. Neither "experience," _i.e._ a general conviction which results from the frequent repetition of similar perceptions, nor thought can arise in any animal in which sense-stimulation does not leave such "traces" behind it. Similarly "free imagery," the existence of trains of imagination not tied down to the reproduction of an actual order of sensations, is accounted for by the consideration that "chance coincidence" may lead to the stimulation of the heart in the same way in which it might have been stimulated by actual sensation-processes. Sleeping and waking and the experiences of dream-life are likewise due to changes in the functioning of the "common sense-organ," brought about partly by fatigue in the superficial sense-organs, partly by qualitative changes in the blood and "animal spirits" caused by the processes of nutrition and digestion. Probably Aristotle’s best scientific work in psychology is contained in the series of small essays in which this theory of memory and its imagery is worked out. (Aristotle’s language about the "common sensibles" is, of course, the source of our expression "common sense," which, however, has an entirely different meaning. The shifting of sense has apparently been effected through Cicero’s employment of the phrase _sensus communis_ to mean tactful sympathy, the feeling of fellowship with our kind on which the Stoic philosophers laid so much stress.)