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117. (1) OF THE USE OF ANALYSIS IN CRITICISM.- In this case the function of analysis extends to the analysis of all forms of language, from the term to the extended discourse or argument; and, as we have observed, it commences with the latter, which is in fact the most difficult task. For here it is necessary to determine from the loose and inaccurate expressions of ordinary disquisition the precise nature of the conclusions asserted and of the arguments used to establish them; and this task is always difficult, and sometimes impossible. When these matters have been determined it will be necessary also to analyze carefully every syllogism, proposition, or term involved in the course of the reasoning. But this in general, to the trained logician, presents but little difficulty.
§ 118. (2) OF THE USE OF ANALYSIS IN INVENTION.—Strictly speaking, this perhaps extends only to the analysis of the term with a view to simple apprehension, and in a previous passage we have so regarded it. But before this task can be approached, it is necessary for us to determine the nature of the precise questions to be investigated; and this will require an analysis of the facts involved in the investigation, and also of the opinions or theories with regard to those facts casually existing in the mind. For, as will be explained more fully in
the next chapter, the questions demanding investigation are in general determined by the nature and the conditions of the problems involved; and it is essential to a rational investigation that the issues thus involved be clearly ascertained. When the issues or questions are thus determined and logically expressed, our investigation is then narrowed to the determination of the truth of one of two alternative propositions, which are called the thesis and the anti-thesis, and of which one or the other must be true; and thus our task is in general greatly facilitated. The use of this sort of analysis finds its best illustration in the practice of the lawyers, with whom it is an imperative rule that the first step in the investigation of a case must consist in settling the issues. In ordinary discourse this task is almost always neglected, and, as will be seen as we proceed, this is one of the most fruitful sources of fallacy.
§ 119. OF ANALYSIS AND SYNTHESIS GENERALLY.-This subject is one of extreme importance, and to the advanced student should constitute one of the principal subjects for his meditations; but for the purposes we have in view it may be sufficiently developed by a statement of the practical rules by which the reasoner should be governed, which will be given at length in the next chapter.
THE RULES OF LOGIC
OF THE RULES OF LOGIC GENERALLY
120. SCOPE OF THE RULES OF LOGIC.— According to the view we have taken in this essay, inference is only one of the processes of ratiocination. Judgment is also a ratiocinative process, and, like inference, must have its rules by which false or pretended judgments may be distinguished from the real. Moreover, where
our reasoning is not apodictic, we have to use assumed propositions, or assumptions, as premises; and though it is said that Logic is not concerned with the truth or falsity of these, yet this is true only in a qualified sense. For where the falsity of such propositions can be detected by logical processes,-i. e., by definition, judgment, and inference, -it is the function of Logic to condemn and reject them; precisely as in the case of self-contradictory
propositions or propositions otherwise absurd on their face. And in all cases it is its function to determine the logical character of an assumed premise, as being an assumption or hypothesis, and not a judgment.
121. TWOFOLD DIVISION OF THE RULES OF LOGIC.-We propose, therefore, to regard the rules of Logic as legitimately extending to all the processes of ratiocination; and hence as including all rules necessary to direct us in the right use of terms as instruments of ratiocination. They will include, therefore, not only the rules directly governing the process of inference, but also those governing the statement of the premises. The latter which will first be considered will be called the "Rules of Judgment," the former, the "Rules of Inference."
8 122. RULES OF JUDGMENT.-The rules of judgment have for their object, not the forming of right, but the prevention of wrong judgments. Judging is a natural and involuntary operation of the mind. But in the ordinary processes of the mind we are apt to go astray in our judgments; and the object of the rules of judgment is to guard against this infirmity by preventing false judgments, or, where they occur, by detecting them.
123. RULES OF INFERENCE.-The rules. of the syllogism given in a previous chapter
cover all cases of inference except conversion per accidens. But these rules are needlessly complex, and may be advantageously replaced by the rules of substitution, which include all inferences whatever, and are simpler both in their expression and application than the old rules, of which they are but another expression. The rules of the syllogism, however, are of such familiar use by logicians, and are so wrought into the terminology and literature of Logic, that a familiar acquaintance with them is essential to the logical student; for whom also it will be necessary to recognize clearly the substantial identity of the two processes.
$124. FALLACIES OF THE SYLLOGISM, ALL RESOLVABLE INTO FALLACIES OF SUBSTITUTION. This is especially important with reference to the violations of the rules of the syllogism, or, as they are called, the fallacies of the syllogism ($104 et seq.). These are of frequent occurrence, and are familiarly known by technical names; and as these have become firmly established in logical terminology by a use of many centuries, they must, of course, be retained. It will be of advantage to the student, therefore, to have pointed out to him that all these fallacies are simply cases of illicit substitution; which can be readily shown.
Thus, e. g., the fallacy of an ambiguous