[4] Diog. IX. 11, 83.
[5] Hyp. I. 145-147.
[6] Fabricius, Cap. IV. H.
[7] Diog. III. 86.
[8] Pappenheim Gr. Pyrr. Grundzüge, p. 50.
[9] Hyp. I. 163.
[10] Diog. IX. 11, 83.
Following the exposition of the ten Tropes of the older Sceptics, Sextus gives the five Tropes which he attributes to the "later Sceptics."[1] Sextus nowhere mentions the author of these Tropes. Diogenes, however, attributes them to Agrippa, a man of whom we know nothing except his mention of him. He was evidently one of the followers of Aenesidemus, and a scholar of influence in the Sceptical School, who must have himself had disciples, as Diogenes says, οἱ περὶ Ἀγρίππαν [2] add to these tropes other five tropes, using the plural verb. Another Sceptic, also mentioned by Diogenes, and a man unknown from other sources, named some of his books after Agrippa.[3] Agrippa is not given by Diogenes in the list of the leaders of the Sceptical School, but[4] his influence in the development of the thought of the School must have been great, as the transition from the ten Tropes of the "older Sceptics" to the five attributed to Agrippa is a marked one, and shows the entrance into the school of a logical power before unknown in it. The latter are not a reduction of the Tropes of Aenesidemus, but are written from an entirely different standpoint. The ten Tropes are empirical, and aim to furnish objective proofs of the foundation theories of Pyrrhonism, while the five are rather rules of thought leading to logical proof, and are dialectic in their character. We find this distinction illustrated by the different way in which the Trope of relativity is treated in the two groups. In the first it points to an objective relativity, but with Agrippa to a general subjective logical principle. The originality of the Tropes of Agrippa does not lie in their substance matter, but in their formulation and use in the Sceptical School. These methods of proof were, of course, not new, but were well known to Aristotle, and were used by the Sceptical Academy, and probably also by Timon,[5] while the πρός τι goes back at least to Protagoras. The five Tropes are as follows.
| (i) | The one based upon discord. |
| (ii) | The regressus in infinitum. |
| (iii) | Relation. |
| (iv) | The hypothetical. |
| (v) | The circulus in probando. |
Two of these are taken from the old list, the first and the third, and Sextus says that the five Tropes are intended to supplement the ten Tropes, and to show the audacity of the Dogmatics in a variety of ways.[6] The order of these Tropes is the same with Diogenes as with Sextus, but the definitions of them differ sufficiently to show that the two authors took their material from different sources. According to the first one everything in question is either sensible or intellectual, and in attempting to judge it either in life, practically, or "among philosophers," a position is developed from which it is impossible to reach a conclusion.[7] According to the second, every proof requires another proof, and so on to infinity, and there is no standpoint from which to begin the reasoning.[8] According to the third, all perceptions are relative, as the object is colored by the condition of the judge, and the influence of other things around it.[9] According to the fourth, it is impossible to escape from the regressus in infinitum by making a hypothesis the starting point, as the Dogmatics attempt to do.[10] And the fifth, or the circulus in probando, arises when that which should be the proof needs to be sustained by the thing to be proved.