A comparison of the state of speculation in the golden age of debate, with the state of the sciences in the present day, both metaphysical and physical, shows us clearly enough, what are the fields where polemic is most profitable. I set aside the struggles of politics and theology, and look to the scientific form of knowledge, which is, after all, the type of our highest certainty everywhere. Now, undoubtedly, it is in classifying, generalising, defining, and in the so-called logical processes--induction and deduction--that a man can be least left to himself. Until many men have gone over the same field of facts, a classification, a definition, or an induction, cannot be held as safe and sound. In modern science, there are numerous matters that have passed through the fiery furnace of iterated criticism, seven times purified; but there are, attaching to every science, a number of things still in the furnace. Most of all does this apply to the metaphysical or subject sciences, where, according to the popular belief, nothing has yet passed finally out of the fiery trial. In psychology, in logic, in eudaemonics, in sociology, in ethics, the facts are nearly all around our feet; the question is how to classify, define, generalise, express them. This was the situation of Zeno, Socrates, and Plato, for which they invoked the militant ardour of the mind. Man, they saw, is a fighting being; if fighting will do a thing, he will do it well. [MOST USEFUL CLASSES OF DEBATES.] In conformity with this view, the foremost class of debates, and certainly not the least profitable, are such as discuss the meanings of important terms. The genius of Socrates perceived that this was the beginning of all valid knowledge, and, in seeing this, laid the foundation of reasoned truth. I need not repeat the leading terms of metaphysical philosophy; but you can at once understand the form of proceeding by such an instance as "consciousness," debated so as to bring out the question whether, as Hamilton supposed, it is necessarily grounded on knowledge. Next to the leading terms are the broader and more fundamental generalities: for example, the law of relativity; the laws of memory and its conditions, such as the intensity of the present consciousness; Hamilton's inverse relationship of sensation and perception. These are a few psychological instances. The value of a debate on any of these questions depends entirely upon its resolving itself into an inductive survey of the facts, and such surveys are never without fruit.