 The core of the dispute between Arcesilaus and the early Stoics concerns the question of whether there is a criterion of truth. The notion of a criterion is introduced into Hellenistic discussions by Epicurus, who speaks about the kanôn (literally measuring stick) and kritêrion. For Epicurus, a criterion is that evident thing, viz., the content of a sense-perception, against which claims about the non-evident are tested. For example, physics advances claims about non-evident things, such as atoms and void. These are not accessible to the senses, and accordingly, do not count as evident. Perception rules out various physical theories. For example, a physical or metaphysical theory according to which there is no movement can be dismissed because it is in disagreement with the evident.