among different nations.[297] In his attacks on the prevalent theories of ethics, Aenesidêmus again reminds us both of Protagoras and of modern agnosticism. According to him, the general disagreement of mankind proves, among other things, that there is no definable highest good—it is neither virtue, nor pleasure, nor knowledge.[298] In the absence of any dogmatic teaching on the subject at the time when he lived, Protagoras could not give an opinion with regard to the _summum bonum_; but Plato’s famous dialogue represents him as one who, from his point of view, would be unwilling to admit the possibility of introducing fixed principles into conduct; and in like manner, Mr. Herbert Spencer, while accepting the hedonistic principle, gives it such an extremely general signification that he is thrown back on the sceptical principle of leaving everyone free to follow his own inclinations, provided that, in so doing, he does not interfere with the liberty of others. The parallel between Aenesidêmus and Protagoras would become still more complete were it true that the Alexandrian philosopher also sought to base his Scepticism on the Heracleitean theory of Nature, arguing that contradictory assertions are necessitated by the presence of contradictory properties in every object. That Aenesidêmus held this view is stated as a fact by Sextus, whose testimony is here corroborated by Tertullian, or rather by Tertullian’s informant, Soranus. We find, however, that Zeller, who formerly accepted the statement in question as true, has latterly seen reason to reject it. Aenesidêmus cannot, he thinks, have been guilty of so great an inconsistency as to base his Scepticism on the dogmatic physics of Heracleitus. And he explains the agreement of the ancient authorities by supposing that the original work of Aenesidêmus contained a critical account of the Heracleitean theory, that this was misinterpreted into an expression of his adhesion to it by Soranus, and that the blunder was adopted at second-hand by both Sextus and Tertullian.[299]