Such were the leading writers and talkers contemporary with Plato, in the dialectical age immediately following on the death of Sokrates. The negative vein greatly preponderates in them, as it does on the whole even in Plato--and as it was pretty sure to do, so long as the form of dialogue was employed. Affirmative exposition and proof is indeed found in some of the later Platonic works, carried on by colloquy between two speakers. But the colloquial form manifests itself evidently as unsuitable for the purpose: and we must remember that Plato was a lecturer as well as a writer, so that his doctrines made their way, at least in part, through continuous exposition. But it is Aristotle with whom the form of affirmative continuous exposition first becomes predominant, in matters of philosophy. Though he composed dialogues (which are now lost), and though he appreciates dialectic as a valuable exercise, yet he considers it only as a discursive preparation; antecedent, though essential, to the more close and concentrated demonstrations of philosophy. [Side-note: Harsh manner in which historians of philosophy censure the negative vein.] Most historians deal hardly with this negative vein. They depreciate the Sophists, the Megarics and Eretrians, the Academics and Sceptics of the subsequent ages--under the title of Eristics, or lovers of contention for itself--as captious and perverse enemies of truth. [Side-note: Negative method in philosophy essential to the controul of the affirmative.] I have already said that my view of the importance and value of the negative vein of philosophy is altogether different. It appears to me quite as essential as the affirmative. It is required as an antecedent, a test, and a corrective. Aristotle deserves all honour for his attempts to construct and defend various affirmative theories: but the value of these theories depends upon their being defensible against all objectors. Affirmative philosophy, as a body not only of truth but of reasoned truth, holds the champion's belt, subject to the challenge not only of competing affirmants, but of all deniers and doubters. And this is the more indispensable, because of the vast problems which these affirmative philosophers undertake to solve: problems especially vast during the age of Plato and Aristotle. The question has to be determined, not only which of two proposed solutions is the best, but whether either of them is tenable, and even whether any solution at all is attainable by the human faculties: whether there exist positive evidence adequate to sustain any conclusion, accompanied with adequate replies to the objections against it. The burthen of proof lies upon the affirmant: and the proof produced must be open to the scrutiny of every dissentient. [Side-note: Sokrates--the most persevering and acute Eristic of his age.]