In fact, Galen’s view of the definition, or fundamental conception, of the hēgemonikon is given much earlier in the work: it is “the source of perception and of voluntary motion” (PHP II.3, 110, also VII.1, 430). It is on this conception, which Galen takes to be universally agreed, even by his opponents, that the greater part of the argument against those (cardiocentric, monist) opponents and in favour of Galen’s (encephalocentric, tripartite) theory depends: cardiocentrism is shown to be wrong on the basis of that agreed conception. Thus, Galen’s demonstration in PHP proceeds largely by taking the universally agreed conception of a term (hēgemonikon), and showing that a particular factual proposition about that term—namely, that the hēgemonikon is in the brain—follows from that conception, in conjunction with further evidence (partly empirical evidence, partly further agreed conceptions). The process of reasoning from that universally agreed perception to the cast-iron syllogism with which Galen presents us at the culmination of the argument, however, is a complex one, much less clearly accessible to representation in formal logical terms. The relative role of “starting-points taken directly from the ousia of the subject” and empirical observations or further evidence seems much more complex than the theoretical syllogistic framing of them would allow.