[Footnote 37: Plato, Menon, p. 80 A. [Greek: na/rkê thalassi/a]. Compare what I have said above about the Ion, ch. XVII., p. 128.] [Footnote 38: Plato, Menon, p. 80 D.] [Side-note: Great question discussed among the Grecian philosophers--criterion of truth--Wherein consists the process of verification?] Here we find explicitly raised, for the first time, that difficulty which embarrassed the different philosophical schools in Greece for the subsequent three centuries--What is the criterion of truth? Wherein consists the process called verification and proof, of that which is first presented as an hypothesis? This was one of the great problems debated between the Academics, the Stoics, and the Sceptics, until the extinction of the schools of philosophy.[39] [Footnote 39: Sokrates here calls this problem an [Greek: e)ristiko\s lo/gos]. Stallbaum (in his Prolegom. to the Menon, p. 14) describes it as a "quæstiunculam, haud dubie e sophistarum disciplinâ arreptam". If the Sophists were the first to raise this question, I think that by doing so they rendered service to the interests of philosophy. The question is among the first which ought to be thoroughly debated and sifted, if we are to have a body of "reasoned truth" called philosophy. I dissent from the opinion of Stallbaum (p. 20), though it is adopted both by Socher (Ueber Platon, p. 185) and by Steinhart (Einleitung zum Menon, p. 123), that the Menon was composed by Plato during the lifetime of Sokrates. Schleiermacher (Einleitung zum Gorgias, p. 22; Einleitung zum Menon, pp. 329-330), Ueberweg (Aechth. Plat. Schr. p. 226), and K. F. Hermann, on the other hand, regard the Menon as composed after the death of Sokrates, and on this point I agree with them, though whether it was composed not long after that event (as K. F. Hermann thinks) or thirteen years after it (as Schleiermacher thinks), I see no sufficient grounds for deciding. I incline to the belief that its composition is considerably later than Hermann supposes; the mention of the Theban Ismenias is one among the reasons rendering such later origin probable. Plato probably borrowed from the Xenophontic Anabasis the name, country, and social position of Menon, who may have received teaching from Gorgias, as we know that Proxenus did, Xen. Anab. ii. 6, 16. The reader can compare the Einleitung of Schleiermacher (in which he professes to prove that the Menon is a corollary to the Theætêtus and Gorgias, and an immediate antecedent to the Euthydêmus,--that it solves the riddle of the Protagoras--and that it presupposes and refers back to the Phædrus) with the Einleitung of Steinhart (p. 120 seq.), who contests all these propositions, saying that the Menon is decidedly later than the Euthydêmus, and decidedly earlier than the Theætêtus, Gorgias, and Phædrus; with the opinions of Stallbaum and Hermann, who recognise an order different from that either of Steinhart or Schleiermacher; and