necessity, because it seemed the fairest way of presenting what could be said on both sides of the question. I hope it may have the good fortune to keep alive the interest of the reader, after he has perused the previous chapters. One disadvantage of all positive writing or discourse is that there is no one to confute, to contradict, or to maintain the negative. At the bar, and in some public assemblies, there is an antagonist; and truth is elicited by the collision. But in didactic writing, especially on a philosophical topic, it is best to introduce an antagonist, and to make him speak in his own person. Two of the best thinkers of our time have forcibly stated the advantage--the necessity, in short--of personal debate. Mr. John Stuart Mill, in his essay on Liberty, observes that-- "The loss of so important an aid to the intelligent and living apprehension of a truth as is afforded by the necessity of explaining it to or defending it against opponents, though not sufficient to outweigh, is no trifling drawback from the benefits of its universal recognition. Where this advantage can not be had, I confess I should like to see the teachers of mankind endeavoring to provide a substitute for it; some contrivance for making the difficulties of the question as present to the learner's consciousness as if they were pressed upon him by a dissentient champion eager for his conversion. "But instead of seeking contrivances for this purpose, they have lost those they formerly had. The Socratic dialectics, so magnificently exemplified in the dialogues of Plato, were a contrivance of this description. They were essentially a discussion of the great questions of life and philosophy, directed with consummate skill to the purpose of convincing any one, who had merely adopted the commonplaces of received opinion, that he did not understand the subject--that he as yet attached no definite meaning to the doctrines he professed, in order that, becoming aware of his ignorance, he might be put in the way to attain a stable belief, resting on a clear apprehension both of the meaning of doctrines and of their evidence. The school disputations of the middle ages had a similar object. They were intended to make sure that the pupil understood his own opinion, and (by necessary correlation) the opinion opposed to it, and could enforce the grounds of one and confute those of the other. The last-mentioned contests had, indeed, the incurable defect that the premises appealed to were taken from authority, not from reason; and as a discipline to the mind they were in every respect inferior to the powerful dialectics which formed the intellects of the 'Socratici viri.' But the modern mind owes far more to both than it is generally willing to admit; and the present modes of instruction contain nothing which in the smallest degree supplies the place either of the one or of the other.... It is the fashion of the present time to disparage negative logic--that