more obvious when it comes to reading the names of the politicians, considering whether they are good likenesses, and feeling what a fine fellow one of them looks and what unmitigated villainy is stamped upon the features of the other. None of this counts as sensation, yet it is part of a man’s spontaneous reaction to an outside stimulus. It is evidently difficult to avoid a certain artificiality in distinguishing between the effects of experience and the rest in a man’s reaction to a stimulus. Perhaps we could tackle the matter in a slightly different way. We can distinguish stimuli of different sorts: to the eye, the ear, the nose, the palate, etc. We can also distinguish elements of different sorts in the reaction: visual elements, auditory elements, etc. The latter are defined, not by the stimulus, but by their intrinsic quality. A visual sensation and a visual image have a common quality which neither shares with an auditory sensation or an auditory image. We may then say: a visual image is an occurrence having the visual quality but not due to a stimulus to the eye, _i.e._ not having as a direct causal antecedent the incidence of light-waves upon the retina. Similarly an auditory image will be an occurrence having the auditory quality but not due to sound-waves reaching the ear, and so on for the other senses. This means a complete abandonment of the attempt to distinguish psychologically between sensations and images; the distinction becomes solely one as to physical antecedents. It is true that we can and do arrive at the distinction without scientific physics, because we find that certain elements in our integral reactions have the correlations that make us regard them as corresponding to something external while others do not--correlations both with the experience of others and with our own past and future experiences. But when we refine upon this common-sense distinction and try to make it precise, it becomes the distinction in terms of physics as stated just now. We might therefore conclude that an image is an occurrence having the quality associated with stimulation by some sense-organ, but not due to such stimulation. In human beings, images seem to depend upon past experience, but perhaps in more instinctive animals they are partly due to innate cerebral mechanisms. In any case dependence upon experience is not the mark by which they are to be defined. This shows how intimate is the dependence of traditional psychology upon physics, and how difficult it is to make psychology into an autonomous science.