d. The fourth trope is that of Pre-supposition (ὀ ἐξ ὑποθέσεως): “When the dogmatists see that they are thrown back into the infinite, they put forward something as principle which they do not prove, but wish to have conceded to them simply and without proof:” that is an axiom. If the dogmatist has the right to pre-suppose an axiom as unproved, the sceptic has equally the right, or, if we choose to say so, equally no right, to pre-suppose the opposite as unproved. One is as good as the other. Thus all definitions are pre-suppositions. For instance, Spinoza pre-supposes definitions of the infinite, of substance, of attribute, &c.; and the rest follows consistently from them. Nowadays men prefer to give assurances and speak of facts of consciousness. e. The last trope is that of Reciprocity (διάλληλος), or proof in a circle. “That which is dealt with is grounded on something which itself again requires something else as its ground; now that which has been said to be proved by it is used for this purpose, so that each is proved through the other.” When we would avoid infinite progression and the making of pre-suppositions, we use again that which was proved to prove its own proof. To the question, “What is the ground of the phenomenon?” the reply is “Power,” but this is itself merely deduced from the moments of the phenomenon. Now Sextus shows (Pyrrh. Hyp. I. c. 15, §§ 169-177) in the following way that, speaking generally, all sceptical investigations pass into these five modes of reasoning; and from this it is likewise clear that Scepticism is not really a reasoning against anything from reasons which can be found, which quick-wittedness discovers in the particular object, but that it has a profound knowledge of the categories. (α) “The object before us is either one felt” (according to Epicurus), “or one thought” (according to the Stoics). “But however it may be determined, there always is a difference of opinion respecting it,” and specially of sophic opinions. This is the first trope. “For some believe what is felt and others what is thought to be alone the truth,” _i.e._ the criterion; “others, however, again accept partly what is thought and partly what is felt.” There consequently is a contradiction present here. “Now is it possible to harmonize this contradiction or not? If not, we must withhold our judgment. But if it is to be solved, the question is, ‘How shall we decide?’” What is to contain the criterion, the standard, the implicit? “Is what is felt to be judged by what is felt, or by what is thought?” (β) Either side, individually considered as the implicit, passes, according to the Sceptics, into the infinite; but this is a description which must necessarily be proved on its own account. “If what is felt is to be judged by what is felt, it is allowed (since feeling is in question) that this sensation requires another sensation as its reason;” for the conviction of its truth is not without contradiction.