Protagoras makes man the measure of all things, of things 216 that are that they are, and things that are not that they are not, meaning by measure, criterion, and by things, events, that is to say really, man is the criterion for all events, of things that are that they are, and of things that are not that they are not. And for that reason he accepts only the phenomena that appear to each man, and thus he introduces relation. Therefore 217 he seems to have community with the Pyrrhoneans. He differs, however, from them, and we shall see the difference after we have somewhat explained how things seemed to Protagoras. He says, for example, that matter is fluid, and as it flows, additions are constantly made in the place of that which is carried away; the perceptions also are arranged anew and changed, according to the age and according to other conditions of the body. He says also, that the reasons of all phenomena 218 are present in matter, so that matter can be all that it appears to be to all men as far as its power is concerned. Men, however, apprehend differently at different times, according to the different conditions that they are in; for he that is in a natural condition will apprehend those qualities in matter that can appear to those who are in a natural condition, while on 219 the contrary, those who are in an unnatural condition will apprehend those qualities that can appear to the abnormal. Furthermore, the same reasoning would hold true in regard to differences in age, to sleeping and waking, and each of the other different conditions. Therefore man becomes the criterion of things that are, for all things that appear to men exist for men, and those things that do not appear to any one among men do not exist. We see that he dogmatises in saying that matter is fluid, and also in saying that the reasons for all phenomena have their foundation in matter, while these things are unknown, and to us are things regarding which we suspend our judgment. CHAPTER XXXIII. _In what does Scepticism differ from the Academic Philosophy?_