Chapter 18
Logical Fallacies
Giovanna Fogli
The need to classify and categorize different kinds of faulty reasoning dates back to Ancient Greece, to the intellectual debate taking place in V century Athens and to the tradition of public speaking that accompanied the evolution of political and civil life of the polis. From Plato’s Dialogues (such as the Euthydemus) to Aristotle’s writings on Rhetoric and On Sophistical Refutations, (De Sophisticis Elenchis), counter-arguing instructions strategies included classification and naming of various types of fallacious reasoning.
Reasoning, Validity and Truth
We call ‘logical fallacy’ a faulty argument – that is to say an argument that presents either an invalid (as in deductive reasoning) or a weak conclusion (as in inductive reasoning): “A fallacious argument, as almost every account from Aristotle onwards tells you, is one that seems to be valid but is not so” (Hamblin, 1970, p. 12). Learning how to recognize logical fallacies will help you not only to identify and adequately counter – argue other people’s fallacious reasoning but most importantly will allow you to properly structure your own arguments, avoiding erroneous reasoning and faulty argumentation that may weaken your written work and invalidate an otherwise true conclusion. Now, before we discuss them in detail, we should note that if it is true that logical fallacies are tools we use to evaluate poor reasoning, it is also true that Fallacy Theory is part of Informal Logic. This means that weak reasoning in faulty arguments is not always purely due to a faulty and perhaps mechanical connection between premises and conclusion; it often relies as well on the manipulation of rhetorical elements (e.g., ethos or pathos). We should not expect from the categorization of logical fallacies either mathematical precision or the exact workings of formal logic. In fact, as you evaluate problematic arguments, you may conclude that more than one fallacy may be responsible for the errors in the argument and that the distinction between, say, a straw man and a non-sequitur, is not always clear cut. However, you will find that, in most cases, faulty reasoning is the result of an incorrect deduction, an improper inference or a verbal ambiguity. Very often the question is more about the validity or the weakness of the argument than about objective truth, especially when your exploration of the text takes into consideration its rhetorical aspects and therefore the issues of persuasion and belief come into place.
To better understand logical fallacies, it is helpful to recall briefly the distinction between deductive and inductive reasoning. In deductive reasoning we derive a specific conclusion from general premises while in inductive reasoning we infer a general conclusion from specific premises. In deductive reasoning, when the deduction is properly conducted, and it is therefore called valid, the truth of the premises guarantees the truth of the conclusion (since we derive a specific conclusion from a general true principle) while inductive reasoning does not offer the same strict connection between truth and validity, and the truth of the premises does not guarantee the truth of the conclusion – a sound inference based on true premises is only probably true. Classic examples of deductive reasoning are categorical syllogism (e.g. “all as are bs; I am an a; therefore I am a b” or “all humans are mortal; I am a human; I am mortal”) and hypothetical syllogisms (“if a then b”).
The complex connection between validity and truth (a changing one as well, especially when it comes to scientific arguments), and the fact that they are NOT the same thing, can be illustrated by the example of Galileo who used his observation of tides to defend Copernicus’s theory of the earth’s movement. For this, Galileo was accused by his opponents of having affirmed the consequent, an invalid form of conditional syllogism. Here is how the defenders of the Ptolemaic system re-formulated Galileo Galilei’s reasoning:
First Premise: If the Earth moves, we would observe tides.
Second Premise: We observe tides.
Conclusion: Therefore, the Earth moves.
Even though Galileo was right in sustaining Copernicus’ position and rejecting the Ptolemaic system, this formulation used the consequent (the observation of tides) to prove the antecedent (earth’s movement) indeed offering a fallacious form of hypothetical syllogism1.
Definition of fallacy: material vs. verbal vs. emotional appeal;
The Stanford Encyclopedia of Philosophy defines a logical fallacy as “a pattern of poor reasoning which appears to be (and in this sense mimics) a pattern of good reasoning (see Hansen [2002]).” As we pointed out before, you should be able to recognize informal fallacies in order to avoid them in your own writing; you ability to recognize different kinds of faulty reasoning is an essential part of any counter arguing strategy (required in many HCC assignments, from the Oral Presentation on Goethe’s Faust, to Prof. Thomas’s assignment on a Supreme Court Case to Prof. Bencivenga’s discussion of Galileo Galilei)
There are many, lengthy classifications of types of fallacies. Our goal here is by no means to offer a complete taxonomy but rather to offer you an agile, however basic, interpretive tool. As we discussed, a deductive fallacy consists of an invalid conclusion while an inductive fallacy may be defined as a weak conclusion. Fallacies can also be categorized as follow:
Material fallacies have to do with the content of the argument, the fact, and they can concern a) evidence: the argument does not provide enough support (as in the case of a Hasty generalization); b) Relevance: that which is indicated as supporting evidence is in fact not relevant to the conclusion (as in the case of a Red Herring)
Verbal fallacies concern ambiguity (double meaning), inconsistency, circularity as in Begging the questions or Equivocation
Improper emotional appeal happens when an improper use of Rhetoric aims at causing an emotional response diverting attention from the weakness of the argument (as in Appeal to fear)
Types of Fallacies
Affirming the consequent (already mentioned in our discussion of conditional syllogism, but included here as well as a very frequent kind of problematic reasoning): In an if clause the ‘if’ part is called ‘antecedent’ and the ‘then’ part ‘consequent’ – to affirm the validity/truth of the antecedent based on evidence supporting the consequent is to commit a fallacy. E.g.: “If she’s an Opera Singer, she sings well. She does sing well. Therefore she is an Opera Singer.” However, she might be a pop singer or not a singer at all.
Hasty generalization: faulty reasoning due to jumping to a generalized conclusion drawn with not enough necessary evidence. E.g., “Smoking is deadly. My uncle smoked and he died of lung cancer”: smoking might indeed be deadly, but the death of your uncle alone is not sufficient evidence. Or, “Last year I took Logic and I got a C. So did my friend and my roommate. It is impossible to get an A in Logic!” Logic might indeed be difficult, but the fact that you and your roommate did not get an A does not make it impossible for others.
Faulty causality (Post hoc/propter hoc “After this, therefore because of this”): a sequence of events is improperly turned into a causal chain (just because event A happens before event B, we cannot hastily infer that B happens because of A). E.g., “Protestantism is an imperialistic religion. Right after the Protestant Reformation, Europe became imperialistic.”
Begging the question or circular reasoning: in this case premises and conclusions are the same, producing a form of circular reasoning not fallacious per se (as A=A is after all a valid form of reasoning) but rhetorically weak when we consider that this type of reasoning does not allow for any kind of progress in the discussion. E.g., “I can’t lose: I’m a winner” which can be reformulated as “I can’t lose because I can’t lose”.
Equivocation plays on the improper use of two different meanings for the same term. E.g., “My parents make me do yard work every weekend and they do not even pay me. Clearly, they think I am their slave!” The term on which the equivocation plays is ‘work’ (as indicating a household chore and/or exploited labor)
Non sequitur: here, the conclusion does not follow from the premises offering only a very weak inference. E.g., “When I lived at home, I never had to do my own laundry. I don’t see why I have to do it now.” The fact that you were lucky enough never to do your own laundry before college is not relevant to your claim that someone else should do it for you now.
Red herring: A red herring is a very smelly fish and the name of this fallacy conveys the idea of throwing someone off the searching path. In this fallacy a severely distracting element diverts from the logical conclusion. E.g. “Our professor should only give As and Bs as the key to successful learning is participation and happy students participate more willingly.” Happy students may be more willing to participate but this consideration is irrelevant when establishing grading criteria and evaluating student work.
Straw man: Setting up a straw man is another form of ‘distracting logic’ where the irrelevant element is found in the opponent’s position. The fallacy is committed when one, e.g. through exaggeration or misrepresentation or simply lying, attributes a false position to the opponent and then attacks it. E.g., “Proponents of extending unemployment benefits are socialists who do not like our capitalist society and want to reward lazy people.”
Ad hominem: the purpose is to distract from the proper conclusion and/or endorse a non valid conclusion attacking the character of the opponent. E.g., “Sarah Palin is a housewife from Alaska: what can she possibly know about politics?”
False analogy: This is an analogy drawn from irrelevant or inconsistent elements – it generalizes one non essential similarity between two objects/situations and extends the analogy to other not similar aspects. E.g., “The University has a budget just like a business. Its President is like a CEO. Therefore, the President’s chief concern should be the bottom line.”
Either-or or false dilemma: improperly limiting to two outcomes when at least another one is possible – very popular strategy in political campaigning. E.g., “Either you believe in God or you have no solid ground for your moral values.”
Slippery slope: improperly anticipating that one occurrence will unavoidably start a series of other occurrences. E.g., “In times of economic crisis, when we allow children of illegal immigrants into our schools, we set our entire public educational system on the path to bankruptcy.”
Bandwagon (Ad Populum): the validity and truth of a conclusion is based on a general consensus. E.g., “I need an I-Phone: everyone has one, therefore it must be necessary…” or “Of course, God exists! The majority of humans believe that she exists.”
Appeal to pity/appeal to fear. These could be called emotional fallacies, as the distraction from an appropriate sound conclusion of the argument comes from an improper use of pathos: the first begs for emotional sympathy to distract from the logical outcome of the argument (“you should give me an extension on this paper since my girlfriend left me and someone stole my IPhone!”). Instead, appeal to fear attempts to instigate fear of the consequences if a certain conclusion is not accepted and/or indorsed (post 9/11 rhetoric offers prime examples of it). E.g., “If we do not enact strict anti-immigration policies, we will see the same violence and beheading taking place across the Border spreading throughout our fair land.”
Appeals to authority: the conclusion is based on an improper ipse dixit ( he/she said it) rather than on premises based on sound evidence (Galileo’s quarrel with the Catholic Church offers plenty of these examples, as at the time Aristotle was the ‘ipse’ in the ‘ipse dixit’…). E.g., “God does not exist. Respected scientists like Stephen Hawkins are convinced of this.”
In addition to informal logic fallacies, you might have heard of Intentional and affective fallacies as well and although these are not logical fallacies per se, at least according to some literary critics, they define erroneous interpretive arguments and you should be careful to avoid them in your writing:
An intentional fallacy consists of basing the interpretation of a text solely on the “intent or purpose of the author.” E.g., “M.H. Kingston feels that ignoring the exact biographical details relevant to her narrative engages the reader at a deeper level” (What makes it a fallacy, is that you cannot possibly know how M.H. Kingston feels, now or when she was writing…)
Affective fallacy happens any time an interpretive claim is based solely on the way the text affects a reader’s emotional response and generally every time your argument is based on the implicit assumption that everyone agrees with your interpretation rather than on clear evidence. E.g., “Clearly, the tale of two fathers in China Men represents a challenge to our innate desire to know about our own origins”. The guilty word here is clearly, which does not explain your point and implies that everyone should agree with you regardless of evidence.
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1 Briefly, a hypothetical syllogism has two valid and two invalid forms. Valid forms are,
Invalid forms (fallacies) are,
Works Cited
Groarke, Leo and Edward N. Zalta (ed.). "Informal Logic." The Stanford Encyclopedia of Philosophy. Winter 2011. Web. 10 Feb. 2013. <http://plato.stanford.edu/archives/win2011/entries/logic-informal/>
Hamblin, Charles Leonard. Fallacies. London: Methuen, 1970. Print.
Hansen, Hans V. “The Straw Thing of Fallacy Theory: The Standard Definition of ‘Fallacy.’” Argumentation 16.2 (2002): 133–155. Print.