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There have many studies of theories of first principles in ancient Platonisms such as the Old Academy, Middle Platonism, and Neoplatonism, and in Platonically inclined religious thinkers such as Philo of Alexandria, Gnosticism, and Christianity. It is generally agreed that monism, the doctrine that all things originate from a single First Principle, is first clearly articulated in the Neopythagoreanism of the first century BCE (Rist 1965), is developed in some strands of Gnosticism in the early 100’s AD, becomes Christian orthodoxy in the second half of the second century (May 1994), and is finally adapted as Platonic orthodoxy after Plotinus (Sorabji 1983). The purposes of this paper is to show how Neopythagoreans could have understand the articulation of monism as the main philosophical project that Plato bequeathed to his followers and to highlight their attempts to explain “how from the One . . . anything else, whether a multiplicity or a dyad or a number, came into existence” (Plotinus V.1.[10].6.5-7).

In his analogy of the divided line, Plato presents the goal of dialectics as the soul rising to “an unconditioned first principle of all” and then descending to the Forms as what follows from It (Republic VI.511b-c). At VII.532a-b, this First Principle is identified with the Good. If the Good is the cause of the existence and essence of the Forms, and if the Forms are the causes of the participated being of sensible things, then the Republic seems to be laying out the metaphysical project of deriving all being from a First Principle. However, Plato’s students, especially Speusippus and Aristotle, consistently present Plato as having taught that such a derivation requires a second First Principle, identified as both the principle of multiplicity and materiality. Only Hermodorus argues that “matter is not a principle,” and that monism is the correct Platonic doctrine (fragments 7-8).

Mainstream Platonism and the doxographical tradition would ascribe two or more first principles to Plato (Dörrie and Baltes 1996). By contrast, the Pythagorean tradition kept open the possibility of monism, for both Aristotle (Metaphysics I.5.986a17-22) and Sextus Empiricus (Against the Physicists 4.261, 282) summarize Pythagorean teachings in which all things are derived from the number one as well the more typical doctrine of primal opposing contraries. In the first centuries BC and AD, monism seems to develop into the dominant Neopythagorean position (Turner 2001). Two versions of On Wisdom, from the Pythagorean pseudepigrapha, present reaching a vision of a single principle, God, who orders the opposing contraries, as the summit of wisdom. Likewise, Eudorus famously presents the Pythagorean doctrine that the transcendent One which is the cause of the one and dyad that are the principles of the contraries, and we have reports from Diogenes Laertius and Photius on Pythagorean monism. How a duality is caused by the One is explained in two ways. First, Moderatus (following Hubler 2012), Theon of Smyrna, and Numenius’s report describe the One as undergoing some kind of process (such as self-privation or self-addition) which results in the dyad. Numenius rightfully rejects these accounts as philosophically unsatisfactory (Testimony 52). Second, Nicomachus of Gerasa, according to the report of his teachings given in Theology of Arithmetic, seems to have used the idea of the coincidence of opposites within the First Principle to defuse the problem. If, following ancient Pythagoreanism, the one is both even and odd, then there is no difficulty in the One eminently precontaining and producing and the principles of both series of contraries. Nicomachus’s possible solution was overlooked by the subsequent pagan Neoplatonic tradition, and has not been adequately recognized as an authentically Pythagorean solution to Plotinus’s question. Plotinus himself would embrace the monistic interpretation of Plato preserved in Neopythagoreanism, but would use elements from Aristotle’s account of the actualization of intellect to explain how a multiplicity can arise from the One without violating its simplicity.