The unprejudiced study of experience, in perceiving and conceiving, such as we have attempted to describe it in the preceding chapters, is liable to be interfered with again and again by certain ideas which spring from the soil of natural science. Thus, taking our stand on science, we say that the eye perceives in the spectrum colours from red to violet. But beyond violet there lie rays within the compass of the spectrum to which corresponds, not a colour perceived by the eye, but a chemical effect. Similarly, beyond the rays which make us perceive red, there are rays which have only heat effects. These and similar phenomena lead, on reflection, to the view that the range of man's perceptual world is defined by the range of his senses, and that he would perceive a very different world if he had additional, or altogether different, senses. Those who like to indulge in far-roaming fancies in this direction, for which the brilliant discoveries of recent scientific research provide a highly tempting occasion, may well be led to confess that nothing enters the field of man's observation except what can affect his senses, as these have been determined by his whole organisation. Man has no right to regard his percepts, limited as these are by his organisation, as in any way a standard to which reality must conform. Every new sense would confront him with a different picture of reality. Within its proper limits, this is a wholly justified view. But if anyone lets himself be confused by this view in the unprejudiced study of the relation of percept and concept, as set forth in these chapters, he blocks the path for himself to a knowledge of man and the world which is rooted in reality. The experience of the essential nature of thought, i.e., the active construction of the world of concepts, is something wholly different from the experience of a perceptible object through the senses. Whatever additional senses man might have, not one would give him reality, if his thinking did not organise with its concepts whatever he perceived by means of such a sense. Every sense, whatever its kind, provided only it is organised by thought, enables man to live right in the real. The fancy-picture of other perceptual worlds, made possible by other senses, has nothing to do with the problem of how it is that man stands in the midst of reality. We must clearly understand that every perceptual picture of the world owes its form to the physical organisation of the percipient, but that only the percepts which have been organised by the living labour of thought lead us into reality. Fanciful speculations concerning the way the world would appear to other than human souls, can give us no occasion to want to understand man's relation to the world. Such a desire comes only with the recognition that every percept presents only a part of the reality it contains, and that, consequently, it leads us away from its own proper reality. This recognition is