Of the six dialogues composed by Eukleides, we cannot speak positively, because they are not preserved. But they cannot have been more refutative, and less affirmative, than most of the Platonic dialogues; and we can hardly be wrong in asserting that they were very inferior both in energy and attraction. The Theætêtus and the Parmenides, two of the most negative among the Platonic dialogues, seem to connect themselves, by the _personnel_ of the drama, with the Megaric philosophers: the former dialogue is ushered in by Eukleides, and is, as it were, dedicated to him: the latter dialogue exhibits, as its _protagonistes_, the veteran Parmenides himself, who forms the one factor of the Megaric philosophy, while Sokrates forms the other. Parmenides (in the Platonic dialogue so called) is made to enforce the negative method in general terms, as a philosophical duty co-ordinate with the affirmative; and to illustrate it by a most elaborate argumentation, directed partly against the Platonic Ideas (here advocated by the youthful Sokrates), partly against his own (the Parmenidean) dogma of Ens Unum. Parmenides adduces unanswerable objections against the dogma of Transcendental Forms or Ideas; yet says at the same time that there can be no philosophy unless you admit it. He reproves the youthful Sokrates for precipitancy in affirming the dogma, and contends that you are not justified in affirming any dogma until you have gone through a bilateral scrutiny of it--that is, first assuming the doctrine to be true, next assuming it to be false, and following out the deductions arising from the one assumption as well as from the other.[30] Parmenides then gives a string of successive deductions (at great length, occupying the last half of the dialogue)--four pairs of counter-demonstrations or Antinomies--in which contradictory conclusions appear each to be alike proved. He enunciates the final result as follows:--"Whether Unum exists, or does not exist, Unum itself and Cætera, both exist and do not exist, both appear and do not appear, all things and in all ways--both in relation to themselves and in relation to each other".[31] [Footnote 30: Plato, Parmen. p. 136.] [Footnote 31: Plato, Parmen. p. 166. [Greek: e(\n ei)/t' e)/stin, ei)/te mê\ e)/stin, au)to/ te kai\ ta)/lla kai\ pro\s au)ta\ kai\ pro\s a)/llêla pa/nta pa/ntôs e)sti/ te kai\ ou)k e)/sti, kai\ phai/netai/ te kai\ ou) phai/netai.--A)lêthe/stata]. See below, vol. iii. chap. xxvii. Parmenides.]