The exposition of the Tropes of Pyrrhonism constitutes historically and philosophically the most important part of the writings of Sextus Empiricus. These Tropes represent the sum total of the wisdom of the older Sceptical School, and were held in high respect for centuries, not only by the Pyrrhoneans, but also by many outside the narrow limits of that School. In the first book of the _Hypotyposes_ Sextus gives two classes of Tropes, those of [Greek: epoche] and the eight Tropes of Aenesidemus against Aetiology. The Tropes of [Greek: epoche] are arranged in groups of ten, five and two, according to the period of the Sceptical School to which they belong; the first of these groups is historically the most important, or the Ten Tropes of [Greek: epoche], as these are far more closely connected with the general development of Scepticism, than the later ones. By the name [Greek: tropos] or Trope, the Sceptic understood a manner of thought, or form of argument, or standpoint of judgement. It was a term common in Greek philosophy, used in this sense, from the time of Aristotle.[1] The Stoics, however, used the word with a different meaning from that attributed to it by the Sceptics.[2] Stephanus and Fabricius translate it by the Latin word _modus_[3] and [Greek: tropos] also is often used interchangeably with the word [Greek: logos] by Sextus, Diogenes Laertius, and others; sometimes also as synonymous with [Greek: topos],[4] and [Greek: typos] is found in the oldest edition of Sextus.[5] Diogenes defines the word as the standpoint, or manner of argument, by which the Sceptics arrived at the condition of doubt, in consequence of the equality of probabilities, and he calls the Tropes, the ten Tropes of doubt.[6] All writers on Pyrrhonism after the time of Aenesidemus give the Tropes the principal place in their treatment of the subject. Sextus occupies two thirds of the first book of the _Hypotyposes_ in stating and discussing them; and about one fourth of his presentation of Scepticism is devoted to the Tropes by Diogenes. In addition to these two authors, Aristocles the Peripatetic refers to them in his attack on Scepticism.[7] Favorinus wrote a book entitled _Pyrrhonean Tropes_, and Plutarch one called _The Ten ([Greek: topoi]) Topes of Pyrrho_.[8] Both of these latter works are lost. [1] Pappenheim _Erlauterung Pyrrh. Grundzugen_, p. 35. [2] Diog I. 76; _Adv. Math._ VIII. 227. [3] Fabricius, Cap. XIV. 7. [4] _Hyp._ I. 36. [5] Fabricius on _Hyp._ I. 36; Cap. XIV. G. [6] Diog. IX. 11, 79-108. [7] Aristocles _Euseb. praep. ev._ X. 14, 18. [8] Fabricius on _Hyp._ I. 36.