This experience, listening to the radio version of "The Green Hills of Earth" was the first form in which I encountered a problem that in the following years continued to haunt much of the work I have done ever since. This problem has a double aspect, since it involves both 'the visibility of the invisible' and, inseparably linked to it, that of the 'invisibility of the visible'. Far from excluding each other, as opposites are commonly expected to do, 'visibility' and 'invisibility' seem here to be inextricably linked, although not simply the same. The prominence, in the story, of repetition and recurrence, indeed of doubling, suggests that another term should be introduced to describe this curious relationship of non-exclusive opposition, that of 'divisibility'. Visibility divides itself into what is visible and what is invisible. And given the fact that this is also a question of life and death, of living and dying, the process of divisibility can be said to produce not just appearances, but 'apparitions' (which in English, unlike its 'false friend' in French, signifies 'ghosts' and not just appearances). Listening to the radio in that darkened bedroom, I think what I experienced was something like the apparition of such divisibility, by which the invisible seemed to become visible, but only by making the visible invisible. Much later I learned that this was a phenomenon - if one can call it that - quite familiar to philosophers and aestheticians who generally tried to interpret it with the use of words such as "fantasy" and "imagination": what Kant, for example, in 'Kritik der reinen Vernunft' calls "productive" as distinct from "reproductive imagination", which does not merely reproduce what one sees but which produces representations of things that were never seen (and perhaps could never be seen). But I never felt that such concepts were capable of accounting for the strange capacity of those invisible 'images' to produce feelings whose intensity seemed in direct proportion to their indistinct and relatively indeterminate - non-objective - quality.