In considering the early theorists above enumerated, there is great difficulty in finding any positive characteristic applicable to all of them. But a negative characteristic may be found, and has already been indicated by Aristotle. "The earlier philosophers (says he) had no part in dialectics: Dialectical force did not yet exist."[12] And the period upon which we are now entering is distinguished mainly by the introduction and increasing preponderance of this new element--Dialectic--first made conspicuously manifest in the Eleatic Zeno and Sokrates; two memorable persons, very different from each other, but having this property in common. [Footnote 12: Aristotel. Metaphys. A. 987, b. 32. [Greek: Oi( ga\r pro/teroi dialektikê=s ou) metei=chon].--M. 1078, b. 25; [Greek: dialektikê\ ga\r i)schu\s ou)/pô to/t' ê)=n, ô(/ste du/nasthai], &c.] [Side-note: Zeno of Elea--Melissus.] It is Zeno who stands announced, on the authority of Aristotle, as the inventor of dialectic: that is, as the first person of whose skill in the art of cross-examination and refutation conspicuous illustrative specimens were preserved. He was among the first who composed written dialogues on controversial matters of philosophy.[13] Both he, and his contemporary the Samian Melissus, took up the defence of the Parmenidean doctrine. It is remarkable that both one and the other were eminent as political men in their native cities. Zeno is even said to have perished miserably, in generous but fruitless attempts to preserve Elea from being enslaved by the despot Nearchus. [Footnote 13: Diogen. Laert. ix. 25-28. The epithets applied to Zeno by Timon are remarkable. [Greek: A)mphoteroglô/ssou te me/ga sthe/nos ou)k a)lapadno\n Zê/nônos pa/ntôn e)pilê/ptoros], &c.] [Side-note: Zeno's Dialectic--he refuted the opponents of Parmenides, by showing that their assumptions led to contradictions and absurdities.]