The common definition of parallax is: the apparent displacement of an object (the shift of its position against a background), caused by a change in observational position that provides a new line of sight. The philosophical twist to be added, of course, is that the observed difference is not simply "subjective," due to the fact that the same object which exists "out there" is seen from two different stations, or points of view. It is rather that, as Hegel would have put it, subject and object are inherently "mediated," so that an "epistemological" shift in the subject's point of view always reflects an "ontological" shift in the object itself. Or, to put it in Lacanese, the subject's gaze is always-already inscribed into the perceived object itself, in the guise of its "blind spot," that which is "in the object more than object itself," the point from which the object itself returns the gaze. "Sure, the picture is in my eye, but me, I am also in the picture": the first part of this Lacan's statement designates subjectivization, the dependence of reality on its subjective constitution, while its second part provides a materialist supplement, reinscribing the subject into its own image in the guise of a stain (the objectivized splinter in its eye). Materialism is not the direct assertion of my inclusion into the objective reality (such an assertion presupposes that my position of enunciation is that of an external observer who can grasp the whole of reality); it rather resides in the reflexive twist by means of which I myself am included into the picture constituted by me - it is this reflexive short-circuit, this necessary REDOUBLING of myself as standing outside AND inside my picture, that bears witness to my "material existence." Materialism means that the reality I see is never "whole" - not because a large part of it eludes me, but because it contains a stain, a blind spot, which signals my inclusion in it.