That the student may attain a real mastery of the art of thinking, it is necessary that the reasons for these maxims should be made clear to him, and that the maxims themselves should be woven into a harmonious code so as to be readily grasped by the mind.
Logic or dialectic is the name of the science from which such rules are drawn. Right reasoning has been obviously the aim of Aristotle in all the books of the Organon except perhaps the first, as it was also of the Stoics, the Lawyers, the medieval summulists, and the modern students of Inductive reasoning, in their additions to Logic. "Dialectica," says the most celebrated treatise on the subject in the middle ages, "est ars artium, scientia scientiarum, ad omnium methodorum principia viam habens. Sola enim dialectica probabiliter disputat de principiis omnium aliarum scientiarum."
Exercise 1. Let the student here write out a fair discussion of the question whether the principles of right reasoning can be investigated. It would seem that these principles must be known before any investigation can be made. In writing this exercise, precision of thought is the first thing to be aimed at, precision in the order of statement the next. All ornament is inadmissible.
A science by which things are tested is necessarily a classificatory science. Thus, every system of qualitative chemical analysis consists in a classification of chemical substances. Accordingly, what we have to study, in the first place, is the classification of inferences. As there are several different systems of qualitative analysis based on different classifications of chemical substances but all valid, so there are different valid systems of logic based on different classifications of inferences. The accomplished reasoner must be familiar with more than one such system.
After a question has been started, opinions may for a while differ. If a sufficiently long course of experience and reasoning will produce a settlement of opinion, this final opinion is the only legitimate aim of experience and reasoning. For this is all that experience and reasoning really tend to. If experience and reasoning will not lead to a final settlement of opinion, they lead to nothing, and can have no legitimate object. In any case, therefore, the only legitimate aim of experience and reasoning is to reach the final opinion, or in other words to ascertain what would be the ultimate result of sufficient experience and reasoning. Now there is no reason to think that there is any possible opinion which sufficient observation and reasoning would not reverse; hence, no absolutely final opinion can be aimed at. But at a sufficiently advanced point of time, there must be some opinion concerning the future settled opinion, which would result from proper reasoning concerning all the experience so far had by men. For at that time if no experience has been had of that concerning which the question is, the inference is that none will be had. If some experience concerning it has been had, reasoning will, from the nature of its rules, be able to draw some inference from it,--whether with great or little confidence. At a sufficiently advanced point of time, therefore, there will be an opinion which ought, from all the facts hitherto observed, according to right reasoning, to prevail.