The concept of perceptual adumbration (Wahrnehmungsabschattung) is so central to the phenomenological theory of perception that the discussion of all problems concerning the phenomenology of perception must take its departure from that concept. The doctrine of perceptual adumbration is based on the obvious fact that every particular perception of a thing is relative to a determinate standpoint and occurs under certain circumstances and conditions. The perceived thing is seen from this or that side, appears under the aspect corresponding to the standpoint at which the perceiving subject happens to be placed. Furthermore, the thing presents itself in a certain orientation relative to the observer and his standpoint as near or far, as at the center of the visual field or more toward the periphery, etc. Finally, the manner of appearance of the perceived thing varies according to whether it is seen in bright daylight or at dusk, in a fog, and so forth.