A fallacy is not merely a _bad_ argument--it is no argument at all. Quite apart from fallacy there is a goodness and badness in arguments, but with this discrimination the dialectician (as such) has nothing to do. Only persons experienced in the matter are competent to decide between good and bad arguments. Hence when the quality of an argument is in question the dialectician takes no part in the debate: he is neither combatant nor umpire. He is at most an impartial president whose chief duty is to see that people do not debate about mere words and foregone conclusions. Granting that a theorem has the qualities of an argument, the dialectician is not competent to say that it is improper or too trivial to be discussed. He is not a judge of what people ought to be interested in. From his better knowledge of what constitutes rational prediction, a dialectician may offer his services to disentangle and render explicit involved and partial arguments. Many people reason well who are yet unable to express themselves coherently. A dialectician should be able to reconstruct an argument from the slightest hint, as a naturalist imagines an animal from a single bone. In ordinary reasoning the arguments are seldom fully expressed, and the reasoners themselves are not always quite conscious of the premises from which they argue. All such suppressed and overlooked assumptions should be brought to light by dialectic, the aim of which is to render reason as self-conscious as possible. Though a dialectician need not be an expert in any department of knowledge, he must know the facts on which an argument is built, otherwise he may be deceived by equivocal language. Reverting to the instance of the vase--the dialectician must have seen both the whole vase and the broken vase, but he need not have any opinion as to whether the proposed handle is the most suitable, or not. That must be left to those who are familiar with vases and who are interested in the restoration of the one in question. The definition here given of the scope and office of dialectic may appear to some too modest. But in reality there is a great deal involved in it. Philosophers have been discussing Reason for twenty centuries or more, and have not produced a satisfactory definition of it. Consequently they cannot decide with any confidence whether a theorem is an argument or a fallacy. The cleverest of them give their sanction to theorems that are demonstrably fallacies. They are evidently judging more by ear than by rule. All this causes confusion of mind and waste of energy.