First demonstration ends in an assemblage of negative conclusions. _Reductio ad Absurdum_, of the assumption--Unum non Multa 96 Second Demonstration 97 It ends in demonstrating _Both_, of that which the first Demonstration had demonstrated _Neither_ 98 Startling paradox--Open offence against logical canon--No logical canon had then been laid down 99 Demonstration third--Attempt to reconcile the contradiction of Demonstrations I. and II. 100 Plato's imagination of the Sudden or Instantaneous--Breaches or momentary stoppages in the course of time _ib._ Review of the successive pairs of Demonstrations or Antinomies in each, the first proves the Neither, the second proves the Both 101 The third Demonstration is mediatorial but not satisfactory--The hypothesis of the Sudden or Instantaneous found no favour 102 Review of the two last Antinomies. Demonstrations VI. and VII. 103 Demonstration VII. is founded upon the genuine doctrine of Parmenides 104 Demonstrations VI. and VII. considered--Unwarrantable steps in the reasoning--The fundamental premiss differently interpreted, though the same in words 105 Demonstrations VIII. and IX.--Analysis of Demonstration VIII. 106 Demonstration VIII. is very subtle and Zenonian 107 Demonstration IX. _Neither_ following _Both_ _ib._ Concluding words of the Parmenides--Declaration that he has demonstrated the Both and the Neither of many different propositions 108 Comparison of the conclusion of the Parmenides to an enigma of the Republic. Difference. The constructor of the enigma adapted its conditions to a foreknown solution. Plato did not _ib._ CHAPTER XXVIII. THEÆTETUS. Subjects and personages in the Theætêtus 110 Question raised by Sokrates--What is knowledge or Cognition? First answer of Theætêtus, enumerating many different cognitions. Corrected by Sokrates 111 Preliminary conversation before the second answer is given. Sokrates describes his own peculiar efficacy--mental obstetric--He cannot teach, but he can evolve knowledge out of pregnant minds 112 Ethical basis of the cross-examination of Sokrates--He is forbidden to pass by falsehood without challenge 113 Answer of Theætêtus--Cognition is sensible perception: Sokrates says that this is the same doctrine as the _Homo Mensura_ laid down by Protagoras, and that both are in close affinity with the doctrines of Homer, Herakleitus, Empedoklês, &c., all except Parmenides _ib._ Plato here blends together three distinct theories for the purpose of confuting them; yet he also professes to urge what can be said in favour of them. Difficulty of following his exposition 114 The doctrine of Protagoras is completely distinct from the other doctrines. The identification of them as one and the same is only constructive--the interpretation of Plato himself 115 Explanation of the doctrine of Protagoras--_Homo Mensura_ 116 Perpetual implication of Subject with Object--Relate and Correlate 118