The sensory qualities of images, their vivacity, clearness, fullness of detail and so on, do not bear any constant relation to their effects. Images differing in these respects may have closely similar consequences. Too much importance has always been attached to the sensory qualities of images. What gives an image efficacy is less its vividness as an image than its character as a mental event peculiarly connected with sensation. Lissette way which no one yet knows how to explain, a relict of sensation and our intellectual and emotional response to it depends far more upon its being, through this fact, a representative of a sensation, than upon its sensory resemblance to one. An image may lose almost all its sensory nature to the point of becoming scarcely an image at all, a mere skeleton, and yet represent a sensation quite as adequately as if it were flaring with hallucinatory vividity. In other words, what matters is not the sensory _resemblance_ of an image to the sensation which is its prototype, but some other relation, at present hidden from us in the jungles of neurology. (Cf. Chapter XIV.) Care then should be taken to avoid the natural tendency to suppose that the more clear and vivid an image the greater will be its efficacy. There are trustworthy people who, according to their accounts, never experience any imagery at all. If certain views commonly expressed about the arts are true, by which vivid imagery is an all-important part of the experience, then these people are incapable of art experiences, a conclusion which is contrary to the facts. The views in question are overlooking the fact that _something_ takes the place of vivid images in these people, and that, provided the image-substitute is efficacious, their lack of mimetic imagery is of no consequence. The efficacy required must, of course, include control over emotional as well as intellectual reactions. Needless perhaps to add that with persons of the image-producing types an increase in delicacy and vivacity in their imagery will probably be accompanied by increased subtlety in effects. Thus it is not surprising that certain great poets and critics have been remarkable for the vigour of their imagery, and dependent upon it. No one would deny the usefulness of imagery to some people; the mistake is to suppose that it is indispensable to all. Articulatory imagery is less noticeable; yet the quality of silent speech is perhaps even more dependent upon these images than upon sound-images. Collocations of syllables which are awkward or unpleasant to utter are rarely delightful to the ear. As a rule the two sets of images are so intimately connected that it is difficult to decide which is the offender. In ‘Heaven, which man’s generation draws,’ the sound doubtless is as harsh as the movements required are cramping to the lips.