Your Mind and How to Use It


Fallacious Reasoning

A fallacy is defined as “an unsound argument or mode of arguing which, while appearing to be decisive of a question, is in reality not so; or a fallacious statement or proposition in which the error is not readily apparent. When a fallacy is used to deceive others, it is called ‘sophistry,'” It is important that the student should understand the nature of the fallacy and understand its most common forms. As Jevons says: “In learning how to do right it is always desirable to be informed as to the ways in which we are likely to go wrong. In describing to a man the road which he should follow, we ought to tell him not only the turnings which he is to take but also the turnings which he is to avoid. Similarly, it is a useful part of logic which teaches us the ways and turnings by which people most commonly go astray in reasoning.”

In presenting the following brief statement regarding the more common forms of fallacy, we omit so far as possible the technical details which belong to text-books on logic.


I. _True Collective but False Particular._–An example of this fallacy is found in the argument that because the French race, collectively, are excitable, therefore a particular Frenchman must be excitable. Or that because the Jewish race, collectively, are good business people, therefore the particular Jew must be a good business man. This is as fallacious as arguing that because a man may drown in the ocean he should avoid the bath, basin, or cup of water. There is a vast difference between the whole of a thing and its separate parts. Nitric acid and glycerin, separately, are not explosive, but, combined, they form nitro-glycerin, a most dangerous and powerful explosive. Reversing this form of illustration, we remind you of the old saying: “Salt is a good thing; but one doesn’t want to be put in pickle.”

II. _Irrelevant Conclusion._–This fallacy consists in introducing in the conclusion matter not contained in the premises, or in the confusing of the issue. For instance: (1) All men are sinful; (2) John Smith is a man; therefore (3) John Smith is a horse thief. This may sound absurd, but many arguments are as fallacious as this, and for the same reason. Or another and more subtle form: (1) All thieves are liars; (2) John Smith is a liar; therefore (3) John Smith is a thief. The first example arises from the introduction of new matter, and the last from the confusion of the issue.

III. _False Cause._–This fallacy consists in attributing cause to a thing which is merely coincident with, or precedent to, the effect. For instance: (1) The cock crows just before or at the moment of sunrise; therefore (2) the cock-crowing is the cause of the sunrise. Or, again: (1) Bad crops followed the election of a Whig president; therefore (2) the Whig party is the cause of the bad crops. Or, again: (1) Where civilization is the highest, there we find the greatest number of high hats; therefore (2) high hats are the cause of civilization.

IV. _Circular Reasoning._–In this form of fallacy the person reasoning or arguing endeavors to explain or prove a thing by itself or its own terms. For instance: (1) The Whig party is honest because it advocates honest principles; (2) the Whig principles are honest because they are advocated by an honest party. A common form of this fallacy in its phase of sophistry is the use of synonyms in such a manner that they seem to express more than the original conception, whereas they are really but other terms for the same thing. An historic example of circular reasoning is the following: (1) The Church of England is the true Church, because it was established by God; (2) it must have been established by God, because it is the true Church. This form of sophistry is most effective when employed in long arguments in which it is difficult to detect it.

V. _Begging the Question._–This fallacy arises from the use of a false premise, or at least of a premise the truth of which is not admitted by the opponent. It may be stated, simply, as “_the unwarranted assumption of a premise, generally the major premise_.” Many persons in public life argue in this way. They boldly assert an unwarranted premise, and then proceed to argue logically from it. The result is confusing to the average person, for, the steps of the reasoning being logical, it seems as if the argument is sound, the fact of the unwarranted premise being overlooked. The person using this form of sophistry proceeds on Aaron Burr’s theory of truth being “that which is boldly asserted and plausibly maintained.”

Bulwer makes one of his characters mention a particularly atrocious form of this fallacy (although an amusing one) in the following words: “Whenever you are about to utter something astonishingly false, always begin with: ‘It is an acknowledged fact,’ etc. Sir Robert Filmer was a master of this manner of writing. Thus with what a solemn face that great man attempted to cheat. He would say: ‘_It is a truth undeniable_ that there cannot be any multitude of men whatsoever, either great or small, etc., but that in the same multitude there is one man among them _that in nature hath a right to be King of all the rest–as being the next heir of Adam_!'”

Look carefully for the major premise of propositions advanced in argument, spoken or written. Be sure that the person making the proposition is not “begging the question” by _the unwarranted assumption of the premise_.


Hyslop says concerning valid inferences and fallacious ones: “We cannot infer _anything_ we please from any premises we please. We must conform to certain definite rules or principles. Any violation of them will be a fallacy. There are two simple rules which should not be violated: (1) _The subject-matter in the conclusion should be of the same general kind as in the premises_; (2) _the facts constituting the premises must be accepted and must not be fictitious_.” A close observance of these rules will result in the detection and avoidance of the principal forms of fallacious reasoning and sophistry.


There are a number of tricky practices resorted to by persons in argument, that are fallacious in intent and result, which we do not consider here in detail as they scarcely belong to the particular subject of this book. A brief mention, however, may be permitted in the interest of general information. Here are the principal ones:–

(1) Arguing that a proposition is correct because the opponent cannot prove the contrary. The fallacy is seen when we realize that the statement, “The moon is made of green cheese,” is not proved because we cannot prove the contrary. No amount of failure to _disprove_ a proposition really _proves_ it; and no amount of failure to _prove_ a proposition really _disproves_ it. As a general rule, the burden of proof rests upon the person stating the proposition, and his opponent is not called upon to disprove it or else have it considered proved. The old cry of “You cannot _prove_ that it is _not_ so” is based upon a fallacious conception.

(2) Abuse of the opponent, his party, or his cause. This is no real argument or reasoning. It is akin to proving a point by beating the opponent over the head.

(3) Arguing that an opponent does not live up to his principles is no argument against the principles he advocates. A man may advocate the principle of temperance and yet drink to excess. This simply proves that he preaches better than he practices; but the truth of the principle of temperance is not affected in any way thereby. The proof of this is that he may change his practices; and it cannot be held that the change of his personal habits improves or changes the nature of the principle.

(4) Argument of authority is not based on logic. Authority is valuable when really worthy, and merely as corroboration or adding weight; but it is not logical argument. The _reasons_ of the authority alone constitute a real argument. The abuse of this form of argument is shown, in the above reference to “begging the question,” in the quotation from Bulwer.

(5) Appeal to prejudice or public opinion is not a valid argument, for public opinion is frequently wrong and prejudice is often unwarranted. And, at the best, they “have nothing to do with the case” from the standpoint of logic. The abuse of testimony and claimed evidence is also worthy of examination, but we cannot go into the subject here.


But perhaps the most dangerous of all fallacies in the search for truth on the part of the most of us are those which arise from the following:–

(1) The tendency to reason from what we feel and wish to be true, rather than from the actual facts of the case, which causes us unconsciously to assume the mental attitude of “if the facts agree with our likes and pet theories, all is well; if they do not, so much the worse for the facts.”

(2) The tendency in all of us to perceive only the facts that agree with our theories and to ignore the others. We find that for which we seek, and overlook that which does not interest us. Our discoveries follow our interest, and our interest follows our desires and beliefs.

The intelligent man or woman realizes these tendencies of human nature and endeavors to avoid them in his or her own reasoning, but is keenly conscious of them in the arguments and reasoning of others. A failure to observe and guard one’s self against these tendencies results in bigotry, intolerance, narrowness, and intellectual astigmatism.

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