Quaeritur utrum intellectus noster possit multa simul intelligere. Respondeo dicendum quod intellectus quidem potest simul multa intelligere per modum unius, non autem multa per modum multorum.—ST. THOMAS AQUINAS §19. =The Problem of Attention.=—We have now finished our survey of the elementary processes of mind; _all our complex experiences may be analysed into sensations, simple images, and simple feelings_. There has been no special difficulty, so far, in exchanging the common-sense point of view for that of scientific psychology. You may not have realised, positively and intimately, that sensations and simple images are all meaningless; that we have described them simply as processes, as experiences going on; you may have been surprised, in view of the everyday distinction of perception from memory and imagination, to find that the simple image is only doubtfully to be distinguished from the sensation; and you may also have been surprised to learn that the feelings owe their manifold variety of tang and tincture to the sensations with which a simple feeling, pleasant or unpleasant, is blended. There is, however, no real difficulty, when once these things are pointed out, in taking up a scientific standpoint towards the mental elements. As soon as we pass to consider _attention_, the case is changed; we come into definite conflict with popular psychology. =Common sense regards attention as a voluntary concentration of the mind.= For instance: I am sitting at my desk, thinking out and writing down the sentences of this paragraph. As I write, I am subject to all sorts of sensory stimuli; the temperature of the room, the pressure of my clothes, the sight of various pieces of furniture, the sounds from house and street, the scents coming from the room itself or borne in through the open window, organic excitations of various kinds. I could easily let my mind wander; I could lapse into reminiscence, or give the rein to my imagination. Yet I am perfectly well able to ignore all these distractions, and to concentrate upon my self-imposed task. Surely, says common sense, surely the whole situation implies a selective and spontaneous mental activity; I give my attention, of my own accord, to a certain topic that I have myself chosen; I could, if I liked, attend to something wholly different. That is _the nature of attention as it is viewed by common sense_.