9. SUMMARY.
(1) Logic as a science makes known the laws and forms of thought and as an art suggests conditions which must be fulfilled in order to think rightly.
A discussion of the second phase of the definition would be incomplete without a consideration of the negative aspect as well as the positive. Such a viewpoint makes evident the question “What errors must be avoided in order to reason correctly?” An answer to this question is given under the caption of Logical Fallacies.
(2) A logical fallacy is any error in reasoning which has the appearance of correctness.
A fallacy which deceives the writer or speaker himself is termed a paralogism, whereas a fallacy formed for the express purpose of deceiving another is denominated a sophism.
It was the pagan teacher Socrates who taught modern thought to frown upon all forms of sophism; these exist to-day much as they did in the olden time.
(3) Because of disagreement as to definition, and because of inability to prevent an overlapping of species, any logical division of the deductive fallacies must be faulty.
In the division of the deductive fallacies, this treatise retains the phraseology and form worked out by Aristotle, so far as such retention is consistent with the changes incident to the advances of time.
(4) Formal fallacies occur because of careless and improper use of words as arbitrary signs. Formal fallacies are definite and easy of comprehension.
The material fallacies are due to certain inconsistencies in thought and to imperfect ways of interpreting language. They are more subtle and thus more difficult of comprehension than the formal fallacies.
There are material fallacies in thought and material fallacies in language; the former are due to looseness in thinking and the latter to lack of precision in expression.
(5) Fallacies of opposition result most frequently from deriving universals from their corresponding particulars, and from assuming to contradict affirmative universals by negative universals and affirmative particulars by negative particulars.
The common fallacy in the process of obversion consists in using one negative instead of two, whereas the ordinary error of conversion is a matter of distributing an undistributed term.
Fallacies of contraversion must involve either those of obversion or conversion since the process is a combination of the two.
(6) Fallacies in language, because they result from permitting more than one interpretation, may be also denominated fallacies of equivocation.
(1) Ambiguous middle is the fallacy of giving to the middle term a double meaning.
The fallacy of four terms, as the name signifies, exists when the argument has four terms in both form and meaning. Ambiguous middle is a matter of four terms in meaning but only three in form.
(2) The fallacy of amphibology is committed when the given proposition conveys more than one meaning. In order to maintain their prestige the ancient oracles made use of this fallacy.
(3) The fallacy of accent springs from placing undue emphasis on some word or group of words. Newspaper and demagogues are prone to this error, that they may thus create an unfavorable impression towards those whom they oppose.
(4) The fallacy of composition is committed when it is assumed that what is true distributively is likewise true collectively. “All” meaning each one and “all” meaning the whole class often leads to the fallacy of composition.
(5) The fallacy of division is committed when it is assumed that what is true collectively is true distributively.
Division is the converse of composition.
(6) The fallacy of figure of speech is occasioned by assuming that words of the same root have the same meaning.
(7) Fallacies in thought are likewise called fallacies of assumption, because of the tendency to assume as true something which demands further proof.
(1) The fallacy of accident occurs when one reasons from a general truth to an accident case. It is the favored fallacy of the doctrinaire, the reformer and the vender of “cure-alls.”
(2) The fallacy of converse accident occurs when one reasons from an accidental case to a general truth.
Both accident and converse accident are made possiblebecause rules, definitions, maxims, etc., have exceptions. It is easy to confuse division and composition with the fallacies of accident. Division and composition are concerned with the collective and distributive use of terms, whereas the fallacies of accident involve the use of notions in a general and accidental sense. The former represent notions which may be counted or enumerated while the latter concern notions which are logical rather than numerical. Composition and division involve “number of,” accident, “meaning of.”
(3) The fallacy of irrelevant conclusion results when the argument does not squarely meet the point at issue. It is the fallacy of arguing to the wrong point either purposely or ignorantly. This may be accomplished by (1) appealing to sympathy of audience, (2) defaming character of opponent, (3) assuming that the fact is true because of inability to prove the contradictory, (4) gaining point by force, (5) citing authority.
(4) “Non sequitur” is the fallacy of deriving a conclusion which does not follow from the premises. It involves introducing new material in the conclusion.
(5) “False cause” is the fallacy of assuming that because two happenings have occurred together several times the one is the cause of the other. The fallacy is due largely to the exaggerations of fear and superstition.
(6) The fallacy of complex question consists in putting an assumption in the form of a question.
(7) Begging the question is the fallacy of deriving a conclusion from notions which in themselves demand proof.
This fallacy takes the three forms of (1) the assumption of an unproved premise, (2) reasoning in a circle, (3) question begging epithets and appellations.