(Summarized by Br. Lawrence Mary M.I.C.M., Tert., from Logic by Fr. Bittle, Chapter XXI)
Fallacies in Language
Simple Equivocation—words used in different meanings.
Illicit Transition—change of supposition
Example: The intellect is the eye of the soul; but the eye is a material organ; therefore, the intellect is a material organ.
Ambiguous or vague terms
Examples: “Liberty,” “Human rights,” “moral responsibility,” “equal opportunity,” “imperialism,” “racial discrimination”
CORRECTIVE: Insistence on exact definitions will help correct this fallacy
Amphiboly—the use of ambiguous phrases or sentences
Example: This man his father killed.
Fallacy of Composition and Division
Composition—taking jointly what should be taken separately
Example: Two and three are less than four; but two and three are five; ergo, five is less than four.
Division—taking separately what should be taken jointly
Example: All soldiers are an army; but General Pershing was a soldier; ergo, General Pershing was an army.
RULE: If the minor premise and conclusion take the terms in the combined sense, while the major takes the same items in the divided sense, it’s the fallacy of composition. If the minor premise and conclusion take items in a divided sense while the major takes the same items in a conjoined sense, the fallacy is one of division.
Fallacy of Accent of Prosody—false accent or false emphasis in speech
Example: I called him an unmitigated liar: it is true: and I am sorry for it.
Fallacy of Figures of Speech—when a conclusion of identity or similarity in meaning is drawn between one diction and another, due to their similarity of construction. The error is committed when one argues from the form of one word to the form of another word.
Example: Since the meaning of “insecure” is the contradictory of “secure,” one assumes that the meaning of “invaluable must also be the contradictory of “valuable.”
Fallacies in the Matter
These fallacies do not rest on improper and specious use of words but on confusion of ideas and things.
Fallacy of the Accident—consists in the confusion of the accidental and essential characteristics of a thing, so that what is affirmed of something which is adventitious (accidental) to a thing is also applied to the subject itself.
Example: Men and apes are morphologically alike; ergo, they are substantially the same.
Example: Man has intelligence; but intelligence is a Divine Attribute; ergo, man has a Divine Attribute.
Example: That something can be abused by people is only an accident accompanying its proper use. Thus it is not valid to move from the fact that a thing can be abused to the conclusion that it must be prohibited.
Fallacy of Absolute and Qualified Statements—consists in arguing from a statement which is generally true (absolute statement) to a specific case; or from a statement which is true in a special instance (qualified statement) to the general class.
Example: A representative democracy is a good form of government for the United States; therefore it is good for other nations in general.
Example: To condemn an entire group for a crime committed by a few of its members.
Example: To say that it is not permissible to kill one’s fellow man, without taking into account war or self defense.
Example: To say that the Church is Holy, without taking into account that individual men may be sinful.
Ignoring the Issue (ignoratio elenchi)—also called “mistaking the question,” “irrelevant conclusion,” “arguing beside the point,” and “evading the issue.” All of these mean that one either proves what is not in question to be proved, or does not prove what is supposed to be proved, or disproves what has not been asserted.
Example: To deny the immortality of the soul on the grounds that ‘No dead man ever came back.”
Example: To claim that a man did not commit a crime “because he went to church every Sunday.”
Appeal to the people (argumentum ad populum)
Example: To attack the free market system by pointing to poor and starving women and children and offering communism as the solution rather than proving the point.
Appeal to might (argumentum ad baculum)
Example: A company threatens loss of wages or employment if the workers form a labor union.
Appeal to shame or modesty (argumentum ad verecundiam)
Example: Edison was a genius in electricity; but his views on the nature of the soul carry no weight, because those problems lie outside of the province of his specialty.
Example: Linus Pauling was a great physicist; Mr. Pauling claimed that vitamin C will cure cancer; ergo, vitamin C will cure cancer.
Appeal to pity (argumentum ad misericordiam)
Example: A defense attorney plays on the pity of the jury by arguing that the criminal had a difficult childhood instead of proving that he did not commit the crime.
Appeal to ignorance (argumentum ad ignorantiam)
Example: Using statistics without proper interpretation to an audience not acquainted with the facts or proper interpretation of the figures.
Appeal to the individual (argumentum ad hominem)
Example: A person heaps abuse or ridicule on his opponent, instead of meeting his arguments.
Example: A person makes the opponent appear ridiculous, to give the impression that his argument is not sound. (This was a technique used by Voltaire against the Catholic Church.)
Example: To use emotional phrasing to discredit an opponent’s position, such as: “slacker,” “draft-dodger,” “yellow belly,” etc.
Invalid extension—a fallacy in which a person attempts to widen the question unduly by giving a more extended application to the opponent’s statement than his moderate claims intend.
Example: A man advocates state ownership of public utilities and his opponent accuses him of advocating for a totalitarian government.
Fallacy of diversion—a fallacy in which one sidesteps the original question and substitutes a different question in its place.
Example: In a trial of communist conspirators, the defense claims that the U.S. jury system is unfair because it is rigged with the rich.
The Fallacy of Begging the Question (petitio principii)—an argumentation in which the very conclusion (question) to be proved is, in some form or other, assumed to be true, or, when the conclusion is proved by a principle whose truth depends on the truth of the conclusion itself.
Using a Synonymous Term.
Example: We say that morphine induces sleep because it has a “soporific effect.”
Tabloid Thinking—using labels, slogans and question-begging epithets, without offering proof for the correctness of the reasoning underlying them. (This can be used for good or for bad.)
Reiteration—based on the principle, if you repeat something often, people will accept it as true, even without proof for the assertion.
Principle wider than the conclusion is assumed to be true
Example: When materialists attempt to prove that the world was not created, by saying that “matter is eternal, therefore the world is eternal” they presuppose the truth of the principle that “matter is eternal.”
Vicious Circle—When a conclusion is proved by a principle used as a premise used in an argument, and later on this same principle is proved by this conclusion used as a premise in a different argument
Example: To prove freedom of the will from the fact of personal responsibility and then later on prove that the fact of personal responsibility from the principle of the freedom of the will.
Unsupported Conclusion—No evidence is offered as proof, but many statements are introduced as “most likely true, “it may be safely assumed,” “there can be no question about the fact,” etc.
Example: Who is not aware of the fact that the western nations are arming for war?
RULE: Since many such statements are simply “gratuitous assertions,” the principle can be applied: “What is gratuitously asserted may be gratuitously denied.”
Fallacy of the Consequent—committed when we use a conditional syllogism and argue from the falsity of the antecedent to the falsity of the consequent, or from the truth of the consequent to the truth of the antecedent.
Example: If he is lazy, he will flunk; he flunked; ergo, he was lazy.
Example: He was not lazy, ergo, he did not flunk.
This is the error often committed in faulty “scientific” reasoning.
Example: If evolution took place, there must be a gradual succession of living forms, ranging from the most primitive to the most specialized; there exists such a gradual succession of living forms; ergo, evolution took place.
Fallacy of the False Cause—we assign a wrong cause to a certain effect. (Superstitions are based on this fallacy. This error occurs frequently in the inductive sciences.)
Example: An aviator carries a rabbit’s foot with him on a flight; the plane plunges to the earth, but he is not killed; therefore it was his lucky rabbit’s foot that saved him.
Fallacy of After This, Therefore on Account of This (post hoc, ergo propter hoc)—simply because one thing follows another does not mean that the former caused the latter.
Example: Man follows the ape in the succession of primates; ergo, man is descended from the ape.
Unwarranted Passage from Probability to Certainty—a fallacy committed when one moves from a probable cause and, without any new evidence, moves to a conclusion asserted to be a certainty.
Example: A general studies the enemy and determines a probable course of action; he forgets that it is probable; then he acts as if the conclusion is certain.