Blumenberg begins by explaining the contrast he wants to draw between symbolism and metaphorics with reference to Fontenelle's critique of geocentrism at the end of the previous chapter. Fontenelle portrays geocentrism's function not as giving an orientating response to a conceptually unanswerable fundamental question (which would make it an absolute metaphor) but as projecting an image of unequal social conventions into the natural world and thus providing an after the fact justification for them. A symbol merely identifies a relationship; it's content has no significance.
Blumenberg spends most of the chapter examining how the circle and the sphere have been used in the history of cosmological metaphorics. The spherical form of the cosmos in Plato assures that it is complete and bounded, in contrast to the threateningly infinite cosmos of Democritus. The model of the cosmos as a stationary, spinning sphere also imitated the combined activity and rest attributed to the divine. This marks a beginning of transfer of attributes of perfection from the Ideas to the cosmos. Aristotle extends this thought to its limit, giving comprehensive scope to the propagation of the ideal of circular motion to nature. The Stoics take this idea even further, attributing even the inner cohesion of objects to a kind of circulation within them. In distinction from Aristotle, however, for the Stoics it is centripetal rather than circular motion which is natural: circular motion results from the displacement of of something from the center due to the natural centripetal movement of some other thing.
Plato requires circular movement for heavenly bodies because he holds that it is most perfectly rational (and hence, the best imitation of the ideal). For Aristotle circular motion is the result of the eros of the first sphere for the unmoved mover. Plotinus synthesizes these accounts, describing circular motion as a physical imitation of the theoretical activity of the unmoved mover ("thought thinking itself"). This circular motion is composite for Plotinus, however. The natural motion of the cosmic body is a straight line; the cosmic soul, in attempting to draw the cosmic body to itself, adds a second component to the motion that results in circular motion. The circular motion that the soul induces in the cosmic body is a metaphor both for the soul's desire for the Mind and for the impossibility of ever consummating it.
122-123: "One cannot talk of 'symbolism' here: the symbol stands in the service of knowledge and must therefore be fixed and static, whereas here we can already detect the highly complex movement that must be represented, indeed 'accomplished', in the geometric expression. Metaphor is capable of movement and can represent movement; there can be no more impressive confirmation of this than Cusansus's self-transcending 'explosive metaphorics', which operates with geometric figures even as it transforms them."
Negative theology does not seek to transmit a body of knowledge, but to train one's intuition in a spiritual process. Cusanus's doubling of circles and spheres is such a process; it begins with steps which are easy to apprehend, but which continue indefinitely is overwhelming. "The aim is to make transcendence something that can be 'experienced' as the limit of theoretical apprehension ..." (123)
Blumenberg does not classify Cusanus's mathematical explosive metaphorics as an absolute metaphor, because it is seen as a positive means to knowledge, not as a means of filling in a vacuum of orientation at the base of thought. But it is similar to absolute metaphors in that its function is pragmatic: it seeks to create a mystical attitude.
Kepler took the traditional metaphorical superiority of the structural center seriously, although the sun rather than the earth now occupied that position for him, and he took equally seriously the metaphorical superiority of circular orbits. This metaphorical realism was a step back from the metaphorical idealization of Copernicus (whose saw man's centrality consisting in his rationality), to say nothing of the acentric universe of Bruno. Nonetheless, this lapse was a key to his systematic accomplishment. In the first place, it allowed him to conceive of a force from the the sun as the source of planetary movement. Furthermore, once the orbits were seen as the result of a solar force, it was possible for him to examine them not as a static idea but as the result of a process, and thus to abandon the ideal assumption of a circular path.
Newton's conception of planetary paths as the result of a composition of different forces itself became a metaphor beyond the realms of astronomy and physics. Montesquieu, Mandeville, and Kant all examine society and history as the result of the composition of actions of individuals or social institutions.
Blumenberg notes that the emergence of modernity can be comprehended in part as and abandonment of circle metaphorics -- and so it is unsurprising that that those, like Nietzsche, who are disenchanted with modernity and seek to overturn it also seek to revive such metaphors.
Reading this, I have been able to see, really for the first time, a sense in which Nietzsche is an authentically anti-modern thinker. I had seen unmasking as the essential move of Nietzschean philosophy, which seemed to make it characteristically modern. Blumenberg's exposition of Nietzsche's metaphorical commitments has complicated my view -- and made me think that Heidegger was not so wrong to see him as the last of the metaphysicians, after all.