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Epitasis and Anesis in Aristotle’s De Caelo 2.6

Stephen Kidd

At De Caelo 2.6, Aristotle claims that all irregular motion has an ἐπίτασις, an ἀκμή and an ἄνεσις. This has traditionally been translated as “acceleration,” “maximum speed” and “deceleration.” However, there are two textual problems, among other problems to be discussed, in translating epitasis as “acceleration,” anesis as “deceleration” and akmē as “maximum speed.” The first is the well-known chestnut of the projectile which reaches its “maximum speed” at the “middle” of its flight: “We can hardly suppose,” one commentator writes, “that Aristotle did not know that a stone from a sling or a lance moves slowest in the middle of its path.” Solutions to this problem have generally been met with scepticism.

The second is a less-discussed issue at the beginning of 2.6 regarding exactly what “all” irregular motion consists of: “all irregular motion has an anesis an epitasis and an akmē,” Aristotle says, not once but twice (288a18-19). This would suggest that all irregular motion is tripartite (anesis, epitasis, akmē). But commentators since Simplicius explain that Aristotle does not actually mean that every example of irregular motion has three parts nor that he is really talking about “all” irregular motion. Instead, he is speaking only about a particular subset of the irregular motion he discusses in the Physics (so not “all” hapasa) and, further, any example of irregular motion will consist of some, but not necessarily of all three parts Aristotle lists in his definition. Simplicius thus has no problem in glossing Aristotle’s “and” with an “or” (ἐπίτασιν ἢ ἀκμὴν ἢ ἄνεσιν, 422.31) – a substitution which would certainly make Aristotle’s claim “more plausible,” as Simplicius’ recent translator suggests. But even though this tinkering with potential tripartition allows the irregular motion discussed here to congrue more easily with Aristotle’s discussion of irregular motion in the Physics, can an “and” so easily become an “or”? Furthermore, since the De Caelo begins with a rather impressive eulogy to the number three (“it is just as the Pythagoreans say...”), should tripartite motion be so easily dismantled in the text?

I would like to propose that Aristotle actually means that all irregular motion consists of three parts and that this idea occurs in a different (likely, earlier) phase of his thought on the subject of irregular motion.