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is true, are chiefly negative; its function is, not so much to teach us to go right, as to keep us from going wrong. But in the operations of the intellect it is so much easier to go wrong than right; it is so utterly impossible for even the most vigorous mind to keep itself in the path but by maintaining a vigilant watch against all deviations, and noting all the byways by which it is possible to go astray that the chief difference between one reasoner and another consists in their less or greater liability to be misled. Logic points out all the possible ways in which, starting from true premises, we may draw false conclusions. By its analysis of the reasoning process, and the forms it supplies for stating and setting forth our reasonings, it enables us to guard the points at which a fallacy is in danger of slipping in, or to lay our fingers upon the place where it has slipped in. When I consider how very simple the theory of reasoning is, and how short a time is sufficient for acquiring a thorough knowledge of its principles and rules, and even considerable expertness in applying them, I can find no excuse for omission to study it on the part of any one who aspires to succeed in any intellectual pursuit. Logic is the great disperser of hazy and confused thinking: it clears up the fogs which hide from us our own ignorance, and make us believe that we understand a subject when we do not. We must not be led away by talk about inarticulate giants who do great deeds without knowing how, and see into the most recondite truths without any of the ordinary helps, and without being able to explain to other people how they reach their conclusions, nor consequently to convince any other people of the truth of them. There may be such men, as there are deaf and dumb persons who do clever things, but for all that, speech and hearing are faculties by no means to be dispensed with. If you want to know whether you are thinking rightly, put your thoughts into words. In the very attempt to do this you will find yourselves, consciously or unconsciously, using logical forms. Logic compels us to throw our meaning into distinct propositions, and our reasonings into distinct steps. It makes us conscious of all the implied assumptions on which we are proceeding, and which, if not true, vitiate the entire process. It makes us aware what extent of doctrine we commit ourselves to by any course of reasoning, and obliges us to look the implied premises in the face, and make up our minds whether we can stand to them. It makes our opinions consistent with themselves and with one another, and forces us to think clearly, even when it cannot make us think correctly. It is true that error may be consistent and systematic as well as truth; but this is not the common case. It is no small advantage to see clearly the principles and consequences involved in our opinions, and which we must either accept, or else abandon
