In the same manner as we teach the Tropes of [Greek: epoche], 180 some set forth Tropes through which we oppose the Dogmatics, by expressing doubt in regard to the aetiology of which they are especially proud. So Aenesidemus teaches eight Tropes, by which he thinks that he can prove all the dogmatic aetiology useless. The first of these Tropes, he said, relates to the character 181 of aetiology in general, which does not give incontestable testimony in regard to phenomena, because it treats of unseen things. The second Trope states that although abundant resources exist by which to investigate the cause of a thing in question, some Dogmatics investigate it in one way only. The third Trope 182 states that the Dogmatics assign causes which do not show any order for things which have taken place in an orderly manner. The fourth Trope states that the Dogmatics, accepting phenomena as they take place, think that they also understand how unseen things take place, although perhaps the unseen things have taken place in the same way as the phenomena, and perhaps in some other way peculiar to themselves. The fifth Trope states 183 that they all, so to speak, assign causes according to their own hypotheses about the elements, but not according to any commonly accepted methods. The sixth states that they often explain things investigated according to their own hypotheses, but ignore opposing hypotheses which have equal probability. The seventh states that they often give reasons for things that 184 not only conflict with phenomena, but also with their own hypotheses. The eighth states that although that which seems manifest, and that which is to be investigated, are often equally inscrutable, they build up a theory from the one about the other, although both are equally inscrutable. It is not impossible, Aenesidemus said also, that some Dogmatics 185 should fail in their theories of causality from other combinations of reasons deducible from the Tropes given above. Perhaps also the five Tropes of [Greek: epoche] are sufficient to refute aetiology, for he who proposes a cause will propose one which is either in harmony with all the sects of philosophy, with Scepticism, and with phenomena, or one that is not. Perhaps, however, it is not possible that a cause should be in harmony with them, for phenomena and unknown things altogether disagree with each other. If it is not in harmony with them, the reason of this will also be demanded of the one who proposed 186 it; and if he accepts a phenomenon as the cause of a phenomenon, or something unknown as the cause of the unknown, he will be thrown into the _regressus in infinitum_; if he uses one cause to account for another one, into the _circulus in probando_; but if he stops anywhere, he will either say that the cause that he proposes holds good so far as regards the things that have been said, and introduce relation, abolishing an absolute standpoint;