This is not the only place in the writings of Sextus which states that Aenesidemus at some time of his life was an advocate of the doctrines of Heraclitus. In no instance, however, where Sextus refers to this remarkable fact, does he offer any explanation of it, or express any bitterness against Aenesidemus, whom he always speaks of with respect as a leader of the Sceptical School. We are thus furnished with one of the most difficult problems of ancient Scepticism, the problem of reconciling the apparent advocacy of Aenesidemus of the teachings of Heraclitus with his position in the Sceptical School. A comparison with each other of the references made by Sextus and other writers to the teachings of Aenesidemus, and a consideration of the result, gives us two pictures of Aenesidemus which conflict most decidedly with each other. We have on the one hand, the man who was the first to give Pyrrhonism a position as an influential school, and the first to collect and present to the world the results of preceding Sceptical thought. He was the compiler of the ten Tropes of [Greek: epoche], and perhaps in part their author, and the author of the eight Tropes against aetiology.[1] He develops his Scepticism from the standpoint that neither the senses nor the intellect can give us any certain knowledge of reality.[2] He denied the possibility of studying phenomena as signs of the unknown.[3] He denied all possibility of truth, and the reality of motion, origin and decay. There was according to his teaching no pleasure or happiness, and no wisdom or supreme good. He denied the possibility of finding out the nature of things, or of proving the existence of the gods, and finally he declared that no ethical aim is possible. [1] _Hyp._ I. 180. [2] Photius 170, B. 12. [3] _Adv. Math._ VIII. 40. The picture on the other hand, presented to us by Sextus and Tertullian, is that of a man with a system of beliefs and dogmas, which lead, he says, to the philosophy of Heraclitus. In strange contradiction to his assertion of the impossibility of all knowledge, he advocates a theory that the original substance is air,[1] which is most certainly a dogma, although indeed a deviation from the teachings of Heraclitus, of which Sextus seemed unconscious, as he says, [Greek: to te on kata ton Herakleiton aer estin, hos physin ho Ainesidemos]. Aenesidemus dogmatised also regarding number and time and unity of the original world-stuff.[2] He seems to have dogmatised further about motion,[3] and about the soul.[4]