By today’s standards, belief in astrology is widely considered to be irrational for being engaged in faulty reasoning; and it was categorized as irrational by E.R Dodds in The Greeks and the Irrational. Dodd’s speculated that the widespread belief in astrology in the Hellenistic era and Late Antiquity was a flight from existential freedom: “better the rigid determinism of astrological Fate than that terrifying burden of daily responsibility” (p 246). This anachronistic approach to rationality removes us further from understanding the phenomena and experience of Greek intellectual life. The inventors and practitioners of astrological methods, whose reasons for believing differed from the population that consulted astrologers, had their own logic expressed by principles of symmetry, harmony, regularity, sameness/difference, and symbolic transference (through sumpatheia). These principles are inherent in the relationship between planets and signs of the zodiac, as well as the movements, speeds, and cycles of planets relative to one another. However, the criticisms of astrological doctrine by Plotinus, Iamblichus, and Hierocles reveal additional layers of rationality and irrationality. In a certain regard, for Iamblichus the problem with birth-time astrology (genethlialogy) is that it is too rational, for the technical rules and discursively derived judgments (to find one’s personal daemon, for instance) introduced human error in an otherwise perfect form of knowledge handed down from gods to humans (DM IX.4). Iamblichus’ redefinition of astrology leaves open questions of how and if it fits into the theurgic theory and practice of later Neoplatonists.
Rationality and irrationality in Platonism also fall along the divisions of the rational and irrational parts of the soul, as well as the sublunary and superlunary realms from which souls ascend and descend. For the theurgical Platonist, there is a paradoxical necessity for irrationality to attain to the supra-rational conceived as four types of madness outlined in the Phaedrus (244b-245b, 265b). Proclus’ interpretation of these types of madness in the Republic commentary can help illustrate what sort of astral knowledge or practice may correspond with these categories. An additional meaning of irrationality is defined by Hierocles as the ‘mindless necessity’ that is believed by the astrologers. However, his version of theurgy in the Carmen aureum commentary invites the possibility of an Iamblichan-style astrology---one that might incorporate katarchical astrology and astral symbolism in the telestics rites.
In this paper I will look at the post-Iamblichean Neoplatonists’ uncomfortable relationship to astrology in light of what they considered to be rational or irrational, and what helped or hindered the soul's ascent to the divine. Through the writings of Proclus, Simplicius and others, I will examine how astrology, in whatever conception necessary, provides knowledge for the Neoplatonist to understand the soul’s immersion in the bonds of necessity and whims of chance. While some aspects of traditional, genethlialogy and katarchical (time-based) astrology remain useful, we may see that a more aesthetic and less rules-based approach to astrological symbolism and significations aligns it with the hieratic arts, particular through visual representation, poetry and music. Music of the spheres, like harmonious sensory music, is divinely rational, though capable of manipulating the irrational parts of the soul for the purpose of the ascent to the divine or the One.