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Updated on August 24, 2014

What is a Logical Fallacy?

In everyday language, the words "fallacy" and "fallacious" are used often to make a charge that what has been claimed is false. This, however, does not capture the logical sense of the words - their meanings as logical terms. If a factual claim is true or false is not a matter of logic or reasoning; it is a matter of not having the right information or some such defect that is related to checking how the world works and how things in the world happen to be. Logic, on the other hand, or reasoning, has to do with assessing arguments, consistency of theories and views, and the status of meanings (if such meanings are logical truths, logical falsehoods, or contingencies.) So, a fallacy in the logical sense is an error in logic - not in ascertaining or representing facts; specifically, a fallacy is an error or defect in an argument, which makes the argument "bad" as an argument. The ideal reasonable person cannot accept such an argument. Even though it can be psychologically persuasive, a fallacious argument does not work - and that is an objective matter as it can be shown. Even if everyone is persuaded that something has been proven successfully, if the proof can be shown to be fallacious - to have some flaw or defect of the kind proofs or arguments have - then there is no proof! Think of a whole village of blind people who agree that something is there - but it is not! This doesn't sound politically correct but let us make sure we are not confused about what is going on. Logic ultimately depends on language - at least, this is a reigning view today. So, here is an example. Even if a whole bunch of people insist that a triangle has four angles, they are still wrong. Given the objective way the meanings of words like "triangle" and "three" and "angles" are fixed in the language, the sentence "a triangle has four angles" has to always be false no matter what anyone or any group of people say. The same happens with arguments but, unlike the case with the statement about triangles, the incorrectness or "badness" of arguments can be very hard to discern or determine. It is scary to know that most of the arguments deployed in advertisements, in political speeches and related environments can be shown to be bad arguments. They are persuasive only psychologically: the ideal reasoner, who could detect the fallacies, would not be persuaded - more correctly, could not possibly be persuaded as a rational person.

Let us recap, with examples, what we have said so far.

In language, we say things like "it is a fallacy that the earth is flat" but this is a statement that happens to be false and the logical term "fallacy" applies not to factual statements but to arguments that have some defect or flaw. Logic studies if arguments work or not. It also studies is a theory or belief - a set of statements - is consistent. Logic also studies the logical status of statements made by sentences. The statement made by the sentence "it is Monday today and it is not Monday today" is: logical falsehood or contradiction; the status of "if it is raining today and we don't have school when it rains, then we don't have school today" is a tautology or logical truth - it can never be false. Sentences like "we have school today" or "we don't have school today" are contingencies: they can be true or they can be false - logic cannot determine that. FALLACIES are pathologies of arguments. The following argument is fallacious but you couldn't count on yourself to detect this. "If it is red, it is colored. If it is not colored, it is blue. Therefore, if it is not red, it is blue."

There is catch. Arguments in language are more often than not presented in elliptic form (this is called an enthymeme, a term made up by Aristotle in another language thousands of years ago): premises, even the conclusion, can be missing and presumed understood to be there given the context. Any time there is a point that is pushed, that is not immediately obvious that one should accept it, and an attempt is made to convince others to accept this point on the basis of other acceptable claims - we have an argument. The point that is being contentious and supported, presumably, is meant as the conclusion. The only way we have a conclusion is by having an argument - the defnitions of these words guarantee this.

For example, when people parading across from a clinic hold signs showing, if they are allowed to do so, images of aborted fetuses, they are pushing an argument. (Remember, "argument" in logic means something like "proof" - it doesn't mean the act of engaging in a dispute or altercation. An argument is a set of sentences one of which is the conclusion and the rest, claimed to be supporting that conclusion, are the premises.) The visual gambit of the protesters is meant to incite a meaning - a statement made by a visual sentence, so to speak. I take it that the statement is "fetuses look human." This is a premise of an argument. The protesters are pushing toward proving something - the conclusion. We don't know if their argument is good or not. But it is an argument. The argument is made visually and, not surprisingly, it is presented in enthymematic form: only one premise (maybe also another premise to the effect that fetuses are dead, obviously, is made.) Other premises are in this argument. And, this being an argument, it has a conclusion. the conclusion is also not stated explicitly - it is not even represented in the visual manner of the protest. What do you, as a reasonable agent, take the conclusion to be? Perhaps, "abortion is morally wrong." This argument needs to be reconstructed. Depending on what side of the debate on this issue you belong, you may wish that their argument is good or bad. But you don't know this. No matter how you FEEL about their position, they could have a good argument. Wishing it to be fallacious has nothing to do with whether it is indeed fallacious. It is more reasonable to assume that in a hard issue like this, there are good arguments on both sides. And, of course, many bad arguments are made too - especially by passionate and unthinking supporters and by propagandists or self-interested parties on both sides. This underscores the need to study LOGIC but the subject is not taught much in schools - and, alas, it is one of the most difficult subjects to study. We will get back to this argument after we have studied fallacies.

As we have said, a fallacy is a defect or flaw affecting an argument, because of which the argument does not work - which means that the conclusion of the argument is not duly supported by the premises. A rational person cannot accept a fallacious arguments.

Arguments come in two varieties: Deductive and Inductive. We will review briefly the meanings of those two terms. Fallacies, accordingly, correspond to the two varieties of argument. Fallacies - flaws - affecting presentation of deductive arguments are called formal fallacies and those undermining inductive arguments are called informal fallacies.

So, we need to get a hold on what those two kinds of arguments are. Whether an argument is deductive or inductive ultimately attests to the kind of relationship that binds premises to conclusion. DEDUCTIVE binding is absolute, unqualifiable and incorrigible: it is logically impossible for the conclusion to be false if the premises are true AND the argument is correct or VALID. In an INDUCTIVE argument, the support offered for the conclusion is assessible in terms of probabilistic degree. Even if the inductive argument made is acceptable as STRONG, it is still a matter of probability whether the conclusion is true on the basis of all true premises.

We notice that what matter in arguments is whether TRUTH is PRESERVED. Given all true premises, is the conclusion true too? Human knowledge would only increase at a crawling pace if we refrained from adding new sentences, which we take as true, on the basis of other, given sentences which we already accept as true. The new sentence, presumably supported by the others, is the conclusion; the supporting, already accepted, sentences, are the premises. When your physician or any other expert you consult moves to a NEW sentence - one inferred from others, a sentence not known from the books they studied or the expertise they have collected - then they are operating as logicians and not as physicians or whatever kind of expert they may be. You see, again, that studying logic is imperative. Logic is tested in some ways in the GMAT, the test for Medical School Admission. It is only in the LSAT, however, for Law School admission, that Logic monopolizes the whole test. Of course, reading comprehension itself (think about it!) testslogic. Remember what we said: when a new sentence (one you don't know if it is true or false at all) is presented, supposed to be supported by other sentences, you are given an argument. You should accept this new sentence (marking accordingly on your multiple choice chart) only if the argument is free of fallacy.

A formal fallacy - a defect of a deductive argument - is also called invalidity. A deductive argument that is correct (whose premises, if true, are guaranteed to support the conclusion) is called valid. You should know, by all means, that DEDUCTIVE reasoning - deductive arguments too - is a matter not of information about the world but it is a matter of what LOGIC FORM the argument has. We recognize a deductive argument by means of checking to see if it has a characteristic logical form. You might think that this is hard, to begin with, but practice improves; moreover, although intuitions are not reliable in logic (unfortunately), there is some intuitive support you can harness when it comes to detecting the form of an argument. Check the examples below:

Here are two arguments, about quite different things, but, in the logical sense, these are two instancces of the same ARGUMENT FORM. These two arguments are valid if and only if this logicaal form they have in common is VALID (if the form, like a cookie cutter, guarantees that the conclusion coming out is true on the basis of all true premises in any argument that has this form.)

1) All tigers are memebrs of the "cat" family. All members of the "cat" family are good hunters. Therefore, all cats are good hunters.

2) All students in this school are hard-working. All hard-working people succeed in their jobs. Therefore, all students in this school are guaranteed to succeed in their jobs.

The two arguments have the SAME LOGICAL FORM. The second doesn't sound right. Yes; at least one premise should not be accepted, perhaps, as being true. The argument is valid, however. People have difficulty grasping this. Validity is a matter of form! The second argument has a form (the same as the first argument), which guarantees true conclusion IF the premises are true. So, the second argument too is valid. But, on account of not having premises all of which are acceptable as true, it is UNSOUND. So, it is a bad argument but the flaw is not logical - from a deductive point of view. The argument does not suffer from a formal fallacy. It must be the other kind of fallacy - the informal one. ("Informal" does not mean "casual" or "anything goes." It means that we don't have a way of tracking it by studying logical forms.) Read the next paragraph to see what happens with our unsound argument. (I take it that the first argument above is valid, of coursee, and it is also sound. This is the most perfect, flaw-free kind of argument you can make. By the way, how do we symbolize the logical form that is common to the two arguments? Here is a possible way: All X are Y; all Y are Z; therefore, all X are Z.

Here is another possible way: All --- are ___; all ___ are \\\; Therefore, all --- are \\\.)

Whether an argument is presented as deductive or inductive depends on the state of mind, on the intentions, of the reasoner but logical analysis imposes an idealized requirement that the reasoner be taken as competent and that, as a matter of logical charity, the best available argument is inserted in defense of putative conclusions. If someone offers an unsound argument, it should be reconstructed as inductive and checked as such.

Inductive arguments cannot be valid or invalid. These are characteristics only of deductive arguments. In an inductive argument, the binding of conclusion to premises is a matter of probability. If the conclusion is quite likely to be true when the premises are true, then the argument is considered relatively strong; otherwise, it is relatively weak. There is no method for assessing relative strenth and weakness of inductive arguments. There are, however, characteristic types of flaws (INFORMAL FALLACIES) that affect inductive arguments. We will briefly study them below.

Formal Fallacies

{X, Y, ...} represent statements (the meanings of sentences that can be used to assert something.) {F, G, ...} represent logical predicates (attributes or properties predicated of some subject.) The symbol "⊬" means "it doesn't follow!"
{X, Y, ...} represent statements (the meanings of sentences that can be used to assert something.) {F, G, ...} represent logical predicates (attributes or properties predicated of some subject.) The symbol "⊬" means "it doesn't follow!"
This fallacy has plagued reasoning throughout history. It is easy to detect in this counterexample: For everyone, there is some date which is his/her birthday. It doesn't follow that there is some date which, for everyone, is his/her birthday.
This fallacy has plagued reasoning throughout history. It is easy to detect in this counterexample: For everyone, there is some date which is his/her birthday. It doesn't follow that there is some date which, for everyone, is his/her birthday.


Is it a matter of opinion whether a logical fallacy is committed or not?

See results

Informal Fallacies

An informal fallacy is a flaw or defect in an inductive argument. We have no logical form or abstract structure to guide us here - as the case was with formal or deductive fallacies. An inductive argument has to be shown, analytically, to be suffering from a defect that makes it not work: the argument doesn't "work" when the truth of the premises does not suffice for accepting the conclusion as true.

An example of an inductive argument is this: "Every duck we have seen so far in this farm has been white. Therefore, every duck in this farm must be white." This is an inductive generalization. Now, consider this: "Every duck we have seen so far in this farm has been white. Therefore, the next duck we will see in this farm is going to be white too." This is an inductive analogy or extrapolation. If we have seen 100 ducks, we have a weaker argument than if we have seen 1000 ducks.

The following argument is also inductive - it is an inductive extrapolation: "The sun has risen every morning. Therefore, the sun must rise tomorrow." Even though the word "must" seems to suggest a knockout kind of argument (a deductive argument), this is not a deductive argument; there is no characteristic logical form to extract. This is an inductive argument. We can't do better - we have no available valid and sound deductive argument to prove that the sun is guaranteed to rise tomorrow. Of course, the inductive argument about the sun rising is very, very strong. It is still an inductive argument, though. There is a probability - even though it is astronomically small! - that the conclusion is false at some point. We take it that the premise of this argument is indeed true. So, the inductive argument we have here is both STRONG (very strong, indeed) as well as COGENT. We could have an inductive argument that is strong but not cogent. For instance: "A million students who have taken our courses so far, have achieved their test-taking objectives. Therefore, you too, after you take our course, are bound to achieve your test-taking objectives, for the same kind of test." Don't be fooled by the word "bound" seeming to guarantee your success. This is not a deductive but an inductive argument. As it goes, it must count as strong -IF the premise is true, then the conclusion is very likely to be true too, given that the high number of students sampled already is very likely to have variation, so as to cover your case too, and it makes it very likely too that you will also succeed in the same way. Now, suppose that the premise is false - not uncommon in advertisement. The argument is still strong (IF the premise is true, the conclusion is quite likely to be true too) but it is not cogent. As such, it is not an acceptable argument.

The defects or flaws of inductive arguments are called Informal Fallacies. It won't do to charge that an argument is fallacious: it has to be shown. In textbook training for Critical Thinking, this is not stressed much; students learn to recognize types of informal fallacies and to check if a given argument commits one of those fallacies. We should keep in mind, though, that there is a BURDEN to show that an argument is fallacious indeed, as charged.

Inductive arguments need to be analyzed one at a time with a view to catching them as defective. This could suggest that we have an open-ended number (infinite perhaps) of possible informal fallacies. It turns out, however, that there is a small number of characteristic types of informal fallacies. These fallacies have names - some of them dating back to Roman times, in Latin. The numnber of big categories of types of informal fallacies is even smaller. There are certain types of errors that seem to generate informal fallacies; within each such category, we can fit the other known types by which informal fallacies are identified. For instance, it is easy to see that too small a sample of ducks (in the argument made above) gives us a weak argument on which to base the conclusion "all ducks in this farm are white". This is called "inadequate sample" and is placed within a broader category we can call "Faulty Induction." We will see below other such broad categories of informal fallacies and also names of some common specific types.

Let us make sure we have the definition of an informal fallacy. We have already spoken of the flaw in the inductive argument but we need a few more elements. (1) A flaw or defect such that, even if the premises are true the conclusion is not acceptably likely to be true. (2) An informal fallacy must also be tempting in the sense that it is not terribly obvious to detect and the average reasonable person could easily "fall" for it. (3) Finally, an informal fallacy must be in principle demonstrable - it must be possible to show analytically that there is an error or, as we have already indicated, it must be possible to carry the burden of showing that a fallacy is committed.

An inductive argument may seem to be committing one of the familiar informal fallacies without it being the case. Analysis is needed, as already emphasized.

The things that can go wrong and seem to be productive of informal fallacies are the following:

  1. Relevance: premises and conclusion should be related in terms of meaning. This should be obvious. If this connection breaks down, we have some type of relevance (better, irrelevance) fallacy. You might think that this should be ridiculously easy to detect but, remember, a fallacy is tempting. You might be surprised to find out that many arguments seem persuasive even though closer attention shows that at least one of the premises is not relevant to what is being argued and what is presumably proven.
  2. Ambiguity. Words and phrases of a language have more than one meaning. Grammatical imprecision can also create reasonable doubt about what meaning is intended out of a possible variety of different meanings. Imagine - which happens a lot! - that words and phrases throughout an argument have more than one meaning. This may be missed; it might not be easy to spot. Then, it seems that we have a good argument but we don't: ambiguity is the problem - the shifting of meaning for a word or phrase. For instance, in Alice in Wonderland, the Queen presents the following argument to Alice: "We can't possibly have pudding today. (this is the conclusion...) The rule says that we can only have pudding any other day. Today, a holiday, is not any other day." The phrase "any other day" is used ambiguously or equivocally: in the first occurrence it means "with one day in between, as in Monday-Wednesday or Tuesday-Thursday, etc.." In the second occurrence, it means "a common or ordinary, not a special, day." Something sounds "funny" about this argument but it is not guaranteed that an argument that suffers from ambiguity is easy to detect as fallacious.
  3. Weak Induction: as mentioned above, there may be problems with the sample (too small or not representative of what we are concluding about).
  4. Dysanalogy: In analogizing from one case to another, there may be good reasons why the case we use in the premises is not sufficiently like the one we conclude about. A great deal of reasoning, from philosophy to constitutional law arguments, is carried out by using analogies. Checking out whether the analogies drawn are sufficiently strong is important.
  5. Probabilistic Fallacies: These are errors in how to think about the working of probabilities. (Notice that if the error can be determined on the basis of the formal theory of probabilities, the Probabilistic Calculus, the fallacy is deductive, not inductive. All reasoning in Mathematics is deductive!)
  6. Presumption: Some premise may be pushed into the argument, but it is not warranted for being accepted as true. We may be tempted to accept it but closer inspection may show that there is no good reason for accepting this premise as true. The premise is simply put down presumptively.
  7. Suppression: Some premise might be left out; had that premise been included - and it is relevant and important - we would see actually that the presented argument is weaker than what it seems as offered. So, suppression of a premise that ought to be included in the argument can wrongly - fallaciously - create the impression that we have a stronger argument than what we actually have.
  8. Causal Fallacies: Drawing conclusions based on how presumably causal relations work is common. A historian once wrote a book, Historians' Fallacies, in which he documented hundreds of examples of fallacies in famous books and textbooks in history, many of which were causal fallacies. For instance, to think that x is the cause of y because x has come first and y followed is a famous causal fallacy - with a Latin name.

Now we turn to specific types of fallacies. Each type fits in one of the above big categories - it might even fit into more than one category. You want to learn the names of some of the common types and to be able to recognize them.

Types of Informal Fallacies 1: Weak Induction, Weak Analogies, Probabilistic Fallacies

Fallacies of Weak or Faulty Induction

Inductive arguments generalize or extrapolate. Inferring that all ducks in the farm are white on the basis of observation of ducks so far is a generalization. Inferring that the next duck, or some duck to be observed in the future, will be white is an extrapolation. Extrapolations can be treated as analogies: an analogy is drawn between the past and the expected future cases of a phenomenon. Analogy is a broader category, though, and it is separately handled below.

  1. Inadequate Sample: Only a few ducks have been observed to be white: therefore, all ducks are white.
  2. Atypical Sample: Ducks from the farm's southwestern corner only have been observed to be white; therefore, all ducks in the farm are white.
  3. Unrepresentative Sample: The ducks the kids were chasing were white; therefore, ducks must be white in this farm.
  4. Irrelevant Sample: Rabbits frmo the farm have been observed to be white; therefore, the ducks of the farm must also be white.
  5. Biased Sample: All the ducks shown us by the farmer's son (who may have a fondness for white ducks, for all we know) were white; therefore, ducks in this farm must be white.
  6. Appeal to Anecdote: Legend has it that the ducks in this farm are famously white; therefore, the ducks of the farm must be white.
  7. Converse Accident or Hasty Generalization: All the ducks we have seen - no matter how many, or how few - have been white; therefore, all ducks must be white.

Weak Analogy or Faulty Analogy

Some famous arguments in the history of philosophy are analogies - and they may well be held under the microscope because it is for analogies to be fallacious. For instance, the Argument of Design, in some of its versions, analogizes from the case in which there is a reasonable expectation that some intelligent and deliberate architect has designed an elaborate structure we suddenly come upon in the wild to the case of the whole universe which also seems like an intricate structure in which the parts fit and seem designed to be doing exactly what needs to be done. In one of the famous critiques of this analogical argument, it may pointed out that the "whole" in the "whole universe" throws a monkey wrench into the drawing of the analogy: any other structure that seems elaborate and purposefully designed is only a part of the whole; isn't this a disanalogy (between part and whole) that undermines the analogy?

An analogy usually runs like this:

  1. All or most observed things that are F are also H1, H2, ...., Hn.
  2. A thing, call it x, has characteristics F as well as H1, H2, ...; it must also have characteristic Hn.

Let us reflect on this to see what are the elements that weaken analogies. Putting down a weak analogical argument is to commit the fallacy of weak or faulty analogy. Specific reasons that are responsible for the weakening of analogies are called disanalogies or dysanalogies.

  • The Number of observed/known/posited cases in the premise - things that have the attributes - might be inadequate.
  • There may be variance within the observed/known/posited cases; for instance, some of the things observed, which are F, are H1, H2, ..., Hj but not Hn.
  • Relative strength of the conclusion: The missing characteristic or characteristics may be likely to be possessed by the unobserved case but this could still be a low degree of probability.
  • Dissimilarities between the observed cases and the unobserved case: for instance, is it perhaps the case that the unobserved case also has attribute G which the observed cases (or most or many of the observed cases) do not have?
  • Relation between observed cases and unobserved case: what if the observed case is very different from the observed cases in some respect - what if the unobserved case has some attribute P which the observed cases don't have? It may only be this one attribute (as with the example above: the universe is a "whole" whereas none of the structures we can ever observe around us can be that.)
  • Relevance between observed cases and unobserved case: some attribute or attributes of teh observed cases or of the unobserved case may be sticking out (as we have seen already): it may be possessed only by the observed cases or only by the unobserved case. The relevance problem comes up if this attribute or attributes make the whole comparison untenable because they indicate that two drastically different things are compared.
  • Availability of (suppressed or previously unknown) weakening premise: for instance, it may turn out after all that H1 causes H2, ..., Hn - which means that we don't have two many attribute s to depend on after all.

Probabilistic Fallacies

  1. Gambler’s Fallacy: Gamblers tend to conclude, fallaciously, that a result becomes less likely to repeat after it has come up once, and that the more extensive the “run” of a result is, the less likely it becomes that the “run” will continue; or that a result is more likely to come up after it has not occurred for a long time. Yet, what result turns up next time does not depend in any way on the result of any preceding “run” - in a fair game.
  2. Lucky Streak Fallacy: Following a streak of favorable results, the conclusion is drawn, fallaciously, that the lucky streak indicates that it is more likely now that the good results will continue (the player is ‘hot.”) This fallacy is related to the Gambler’s Fallacy: they both have as source the failure to realize that fair procedures yield results that are always independent of what preceded.
  3. Multiple Comparisons Fallacy: This is sometimes called the Sharpshooter Fallacy. Consider a shooter who shoots twenty times, for instance, always aiming for the bulls’ eye; having hit it only once, he disregards the nineteen failures and concludes that he has been successful since he managed to hit the target after all. A similar effect is produced, for reasons based on Probablity Theory, when multiple surveys are run. (The name of the fallacy might have originated in the analysis of epidemiological studies in which two different groups are compared to draw conclusions.) If the margin of confidence is set at 95% (or margin of error at 5%) and the items that are compared are independent of one another, then over only 14 such surveys it is more likely than not that a result which seems significant will be obtained; yet, this is merely by chance! So, even though it is tempting to assume that greater accuracy is achieved when more surveys are run to assess distributions, what actually happens is that apparently (but not really) significant results are obtained by chance. This means that studies that have been more thorough might have to be disregarded. This is an apparently paradoxical situation but Probability Theory (by application of the so-called Multiplication Law of probabilities) can show rigorously that this drop in reliability results from running multiple comparisons.
  4. The Base Rate Fallacy: When given both general information about an event of a certain type E and specific information about an instance of E, most people tend to disregard the general information, assuming that specificity trumps general information always. Yet, it can be shown rigorously in Probability Theory, by Bayes Theorem, that the conclusion that only specific information should be used is reached fallaciously. Both types of information should be used (general as well as specific.)
  5. The Fallacy of Conjunction: The probability of a conjunction being true is never greater than the probability that either one of the conjuncts is true. So, it is fallacious, for instance, to argue that it is sufficiently likely that "if we play, we will win" if it is not sufficiently likely that we will win whether we play or not and as a matter of how the game statistics work.

Types of Informal Fallacies 2: Relevance, Ambiguity, Presumption, Suppression

Relevance Fallacies

  1. Ad Ignoratiam: Something is proven, and the proof might be good, but what is proven is not what has been at issue.
  2. Red Herring: Something is thrown into the argument that is not relevant and this triggers a detour to some conclusion that seems convincingly to be following from the premises. For instance, in a debate about the moral status of the fetus, one might introduce premises about the habits of specific women who have had abortions.
  3. Various appeals. Something is appealed to in the premises but analysis would show that what is being appealed to is irrelevant to what is being discussed and argued. For instance, the character of a person might be brought in (standard laywer gambit in the courtroom and inescapable in politics.) The character of the person may be relevant but IF it is not, then this is an argument that suffers from irrelevance. Or the opinion of some celebrity may be appealed to: except that this might be a chemical product, or pharmaceutical, and, of course, the celebrity is no expert (he failed his chemistry class before he dropped out of college altogether!) So, false authority is appealed to. Or you might be expected to be persuaded because public opinion praises some work of art. Or a threat may be made in the premises - but this is irrelevant to how to prove the presented conclusion. Or some detour may be thrown in the argument, taking us to some sensational place that seems to be related to what is being discussed but is not related. More generally, emotions and traditions and prejudices even - they can all be "appealed" to for effect. The argument comes across rhetorically persuasive but it is fallacious - the fallacy is Irrelevance in the broad category but specific appeals have names as we will see below.
  • Appeal to the Person's Character - Ad Hominem or Abusive Ad Hominem: E.g.: Since this person was mean to her dog as a child, you should disregard her testimony in this trial.
  • Appeal to the Person's Circumstances or Group the person belongs to - Ad Hominem Circumstantial: e.g. an argument that "since the writers of a book profit from it, there can't be anything you can believe in it."
  • Tu Quoque ("yoo too"): Arguing that it is permissible or right to do x because those we are doing it to have done it themselves.
  • Appeal to False Authority (ad vericundiam): e.g.: since celebrity x endorses this product, it must be a good product.
  • Appeal to the People (ad populum): e.g. since most people (or the right people, the "cool" crowd) like this or do this, it must be the right thing to do.
  • Appeal to Tradition.
  • Appeal to Emotion.
  • Appeal to Force (ad bacculum): E.g.: if you don't agree with x, you will suffer consequences; therefore, x must surely be right.
  • Appeal to Allegiance, Team Spirit, Patriotism: "my country, right or wrong" or "my team above all, right or wrong."

Ambiguity Fallacies

  1. Equivocation: some word or phrase is used with more than one meaning in the argument, E.g.: Mary knows everything there is to know about the color "blue", having read about it in Braille. But, she is blind, and, so, she cannot possibly know blue. So, she knows and she does not know all about blue. (Not really a successful reduction to a paradox. The argument is fallacious, suffering from equivocation. Two different meanings of the word "know" are used.)
  2. Amphibole: the grammar - punctuation or something else - is used in such a way that more than one meanings can be reasonably understood; so, as with equivocation, there is a shift in meaning throughout the argument. E.g.: This product has been lucky for the stockholders. You should buy it, since it is so lucky. (It is lucky for the stockholders. The occurrence of the word "lucky" in the conclusion should read "lucky-for-you" and then you see that it doesn't follow. It took manipulation of grammar to show this - which is to be expected in the case of amphiboles.)
  3. Accent: emphasis is placed in a manipulative way; this makes it look that we have a successful argument but, if you don't take the distribution of emphasis away, you see that this is not a successful argument after all. E.g.: Some owners say that this is a great car. Therefore, you should buy it. Now try putting the emphasis on another word and see that this is not a successful argument although it seemed tempting because of the accent or emphasis: Some users say that this is a great car. Therefore, you should buy it.

Falacies of Presumption and Suppression

  1. Either/Or Fallacy or False Dichotomy or False Dilemma: A premise has exactly two available options (p or q); but this may be questionable - there may be more options! Usually, the argument goes like this: p or q; not-p; therefore, q. This is a VALID deductive argument. But it is unsound if the premise is false (if there are more options besides p and q.) Charitably taken as an inductive argument, we charge it with the fallacy of false dichotomy (the either/or fallacy or black-and-white fallacy, as it also called sometimes.)
  2. Peitito Principii or Begging the Question: This might be the trickiest fallacy there is. Famous arguments in the history of thought have turned out to be committing some species of this fallacy when closely examined. (An example is the so-called Cartesian Circle in Descartes' Meditations on First Philosophy.) This fallacy is difficult to present, understand and detect. Most students prefer to refer to it as to some form of "circularity" or "circular argument." Here is a simple presentation: we have this fallacy if what is supposed to be proven has been presupposed (is already in the premises, maybe not explicitly but IF you buy into the premises you already buy into what is supposed to be the conclusion anyway!) A wicked manipulator of circular reasoning was Adolf Hitler whose speeches, purporting to prove that he is the embodiment of the ideal will of the German people, already pushed into the premises a role for himself, as Fuhrer, that included his presumed embodiment of the Germans' collective will. The textbook example of this fallacy has someone trying to prove to you that you should believe that there is a God offering as one of the premises that "the Bible says so." But to believe the Bible, you need proof: well, this is because the Bible is inerrant (makes no mistakes, only has truths in it) insofar as it is the work of God. If God is the ultimate author of the Bible - in the PREMISES - then you already buy into what is supposed to be proven (that God exists.) You see the circular reasoning. The term is "begging the question" - although this term also means something different in language today - and the Latin is Petitio Principii.
  3. Complex Question: This involves a question - as the name of the fallacy indicates. Remember that, to have a fallacy, we have to have an argument which has some flaw or defect. The point is that a question is asked in this fallacy to trap the person to whom the question is posed: no matter if she answers "yes" or "no", some label is now attached, something is attributed, to this person but this is a presumption really because we are not given reasons as to why the person has this attribute. The conclusion is that the person so attacked presumably has a certain quality - so we have an argument, as we should have in order to have a fallacy. An example will make this clear. Someone X asks Y: "have you stopped plagiarizing?" No matter what Y answers, the implied conclusion is that Y has been a plagiarist. If Y says "yes", he is admitting to having plagiarized. If he answers "no," it sounds that not only he has plagiarized before but he continues to do so even at the present. Political manipulators can draw a lot of mileage out of this fallacy - as long as the public remains ignorant about how to detect informal fallacies.
  4. Composition: This fallacy is committed when a conclusion is drawn about a whole on the basis of attributes of the parts. E.g.: since all chapters of this book are short, the whole book must be short too.
  5. Division: This fallacy goes in an opposite direction from the previous one (oddly, the two are confused with each other een though the names make it clear which is which.) In this fallacy, a conclusion is drawn about a part or component on the basis of attributes of the whole. E.g.: since the whole book sold well, reprints of isolated chapters should sell well too. It is presumed that whole-parts share something they don't. But, notice, these fallacies could also be placed under Relevance: it is taken to be relevant that something is a component or part with respect to attributing some quality when this is not the case. It is not surprising that the fallacy types we examine here may be classed under more than one of the big categories we have laid out.
  6. Appeal to Ignorance (ad ignoratiam): In this fallacy, a conclusion is drawn to the benefit of the reasoner on the premise that something has not been proven anyway - or has not been verified, or is not known, or it cannot be verified, etc... E.g.: There is no proof there are no aliens; therefore, there must be aliens. It works the other way too - same fallacy: They haven't proven that there are aliens; therefore, there aren't any aliens.
  7. Straw Person (traditionally known as "Straw Man"): This fallacy occurs when some view, position, claim, or even argument is attributed to the opponent; then, the one who makes this felicitous attribution goes on to ... demolish the opposition. Of course, the opposition has been misrepresented in the first place. Consider, as two examples, how parties on both sides of the debate on abortion commit this fallacy: E.g.1: "Of course they would want abortions. They don't want to interrupt having fun and partying all the time." E.g.2: "Of course they would be pro-life. They are religious fanatics anyway." There are serious arguments on both sides of this debate but the ones attributed in these examples to the other side are not!
  8. Slippery Slope: A notorious fallacy - it should be at least; in this fallacy, a conclusion is drawn against some action or practice on the grounds that, presumably, terrible consequences would follow if this action or practice were adopted. E.g.: if we allow civil disobedience, before we know it, everyone will disobey some law or other and we will have chaotic lawlessness and disorder and society will not be functioning anymore. Shockingly, this argument appears in Plato's Crito. But, as with all informal fallacies, examination is needed to check if there is indeed a fallacy. The character in the dialogue, Socrates, thinks that conditions in Athens are already such that people would be sure to disobey some thing or other - because of a relativistic disposition and other habits. If the case can be made that the other unacceptable consequences are quite likely to follow, then we cannot charge slippery slope. But if there blocks down the slope - if other criteria or institutional practices are there to stop the slide - we have a fallacy. In debates about abortion and gay marriage, there are famous arguments that seem to raise the specter of this fallacy (what do you think?). In the abortion debate, one popular argument - used by respected intellectuals even - is that alloting status to the fetus would trigger a slippery slope toward attributing such status to unfertilized sperm and eggs. Yet, specific criteria are given as to why the fetus ought to be given a legal status as person (it has a unique genetic signature that carries over into the born baby.) This may or may not be a good criterion but, notice, it is a criterion that does NOT apply to the unfertilized sperm and eggs - the slide is blocked. So, in this case, the pro-choice group seem guilty of slippery slope. In the case of gay marriage, Justice Scalia is fond of claiming that recognizion of a liberty and individual choice stake in gay marriage would open the door (slippery slope again) for incestuous marriage, marriage between human and animal, and other atrocious outcomes. Yet, there must be criteria that would arrest this slide - criteria that do not apply to gay marriage but may apply to other bids for marrying. So, Scalia, though generally recognized as brilliant, seems guilty of a rhetorical lapse into slippery slope in this instance.
  9. Selective Information in the Premises: When important information is suppressed, so that it seems that we have a good argument suporting a conclusion while it doesn't seem so anymore once the missing information is added. Imagine, for instance, if some detective named Sherlock reached a conclusion about who committed a crime; the reasoning seems impeccable but the information is missing (the suppressed premise, whether Sherlock is aware of it or not) that the suspect has a powerful alibi.

© 2014 Odysseus Makridis


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