The best-known part of Stoic epistemology is the doctrine of an ap- pearance which grasps its object (phantasia katale ¯ ptike ¯ ) and functions as a criterion of truth. It was assumed that when people have adequate con- ceptual abilities and their souls are not disturbed, a great number of their perceptual appearances give them an objective guarantee that the appear- ances represent states of affairs correctly. A cataleptic appearance was described as something that ‘seizes us by the hair and pulls us to assent, needing nothing else to achieve this effect or to establish its difference from other appearances’ (Sextus Empiricus, Against the Mathematicians, in Opera, vol. ii, 7.253–7 (LS 40K))