These two forms of visual perception - which we may briefly call: (1) perception of post-images, and (2) perception of co-images - represent successive rungs on a 'spiritual ladder' pointing beyond themselves to a further rung. By the logic of succession this may be expected to consist in some sort of seeing of pre-images, with the characteristic of being a still less physical mode of seeing than the two others. This seeing must be based on an activity of the inner light which will be similar to that in dream by its arising without any stimulus from external light-impressions, yet at the same time there must be no arbitrariness in the contents of this perception. Further, our consciousness in this perceptive activity must be such as to allow us to be in full control of it, as we are of ordinary day-waking seeing.