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. This kind of pure sense-free perception does indeed exist, and it can be aroused by means of a well-ordered training from the dormant state in which it is present in every human being. Anyone who learns to see in this way gains perception of the activity of cosmic light, contacting it directly with his own inner light - that is to say, without mediation of his corporeal eye which is subject to gravity. So this eye-of-the-spirit becomes capable of perceiving the levity-woven archetypes (ur-images), which underlie all that the physical eye discerns in the world of ordinary space. In respect of the intrinsic character of the world-content thus perceived, Rudolf Steiner called this mode of perception, Imaginative perception, or, simply, Imagination. By so doing he invested this word with its due and rightful meaning. From what we found in our optical studies concerning the nature of after-images (Chapter XV), it is clear that the acquisition of Imaginative perception rests on a re-awakening in the eye (and thus in the total organism behind the eye) of certain 'infant' forces which have grown dormant in the course of the growing up of the human being. It thus represents a fulfilment of Thomas Reid's philosophic demand. Consequently we find among the descriptions which Traherne gives of the mode of perception peculiar to man when the inner light, brought into this world at birth, is not yet absorbed by the physical eye, many helpful characterizations of the nature of Imaginative perception, some of which may be quoted here. Consider, in this respect, the following passage from Traherne's poem The Praeparative, quoted earlier. In describing the state of soul at a time when the physical senses are not yet in operation, Traherne says: 'Then was my Soul my only All to me, A living, endless Ey, Whose Power, and Act, and Essence was to see: I was an inward Sphere of Light Or an interminable Orb of Sight, Exceeding that which makes the Days, A vital sun that shed abroad its Rays: All Life, all Sense, A naked, simple, pure Intelligence.''