From the preceding observations springs the utilitarian and practical nature of common perception. Let us attempt now to see of what the elaboration which it makes reality undergo consists. This time I am summing up the fourth chapter of "Matter and Memory". First of all, we choose between the images, emphasising the strong, extinguishing the weak, although both have, a priori, the same interest for pure knowledge; we make this choice above all by according preference to impressions of touch, which are the most useful from the practical point of view. This selection determines the parcelling up of matter into independent bodies, and the artificial character of our proceeding is thus made plain. Does not science, indeed, conclude in the same way, showing us--as soon as she frees herself even to a small extent from common-sense--full continuity re-established by "moving strata," and all bodies resolved into stationary waves and knots of intersecting fluxes? Already, then, we shall be nearer pure perception if we cease to consider anything but the perceptible stuff in which numerically distinct percepts are cut. Even there, however, a utilitarian division continues. Our senses are instruments of abstraction, each of them discerning a possible path of action. We may say that corporal life functions in the manner of an absorbing milieu, which determines the disconnected scale of simple qualities by extinguishing most of the perceptible radiations. In short, the scale of sensations, with its numerical aspect, is nothing but the spectrum of our practical activity. Commonly we perceive only averages and wholes, which we contract into distinct "qualities". Let us disengage from this rhythm what is peculiar to ourselves. Above all, let us strive to disengage ourselves from homogeneous space, this substratum of fixity, this arbitrary scheme of measurement and division, which, to our greater advantage, subtends the natural, qualitative, and undivided extension of images. (We usually represent homogeneous space as previous to the heterogeneous extension of images: as a kind of empty room which we furnish with percepts. We must reverse this order, and conceive, on the contrary, that extension precedes space.) And we shall finally have pure perception in so far as it is accessible to us. There is no disputing the absolute value of this pure perception. The impotence of speculative reason, as demonstrated by Kant, is perhaps, at bottom, only the impotence of an intelligence in bondage to certain necessities of the corporal life, and exercised upon a matter which it has had to disorganise for the satisfaction of our needs. Our knowledge of things is then no longer relative to the fundamental structure of our mind, but only to its superficial and acquired habits, to the contingent form which it takes on from our corporal functions and our lower needs.