SOME SIMPLE RELATIONS OF SENSE DATA
Relations can be perceived and thought about, just as sentienda may be perceived and thought about. The actual experienced world consists of sentienda related to each other in intricate ways, and it contains nothing else. This is true, at least, of the world exclusive of our experienced bodies: there are no experiencible things other than sentienda and relations, unless the feelings which are peculiar to our own organisms are to be classed as something other than sentienda. If there are objective realities in the outside world, besides sentienda and relations, these things are not experienced, and are not "given" in experience, and hence cannot be discussed rationally.
It is probably true that we can seldom, if ever, be conscious of sentienda without relations, or of relations without sentienda related by them. Yet it is possible to be conscious of two sentienda between which there is a specific relation, without being conscious of the relation between them: a relation of difference, for example, as in the case of two sounds differing in pitch. In some cases this failure is merely an accident of perception: a chance direction of attention away from the relation at the moment. Thus, two tones, differing considerably in pitch, may be heard, but the difference may not be observed, although it is of sufficient magnitude to be perceived readily at other times.
In other cases, relations may be imperceptible because the individual has not yet learned to perceive them. Thus, pitch differences which are imperceptible to the unpracticed ear, become readily perceptible after sufficient practice in pitch discrimination.63 In still other cases, relations which actually exist between____________________