A central example of Galenic demonstration is the extended proof of the location of the parts or principles of the soul, in PHP. These are three: the rational (logistikon) or leading-part (hēgemonikon), located, Galen argues, in the brain; the “spirited” (thumoeides), located in the heart; and the desiderative (epithumētikon), located in the liver. Galen claims that the proof that the hēgemonikon resides in the brain (and not, as in particular the Stoics think, the heart) admits of scientific demonstration.