Index of Logical Fallacies and Errors

The following is an alphabetical list of the logical fallacies we study in this course. Each fallacy is followed by a description of the proper method for identifying the fallacy (ID) when it occurs and mistakes commonly made in identifying the fallacy (MID). Hyperlinks connect to examples of the fallacies and their proper identification.

Ad Hominem

    Def.: Attempting to refute a statement by calling attention to the character, actions or personal circumstances of those who support it.

    ID: Identify the statement in question and  identify the attempt to refute the statement by focusing attention on the person who makes it.

    MID:  There is nothing inherently fallacious about attacking people or attempting to discredit them.  An ad hominem occurs only when we do this as part of an attempt to refute his/her view or reasoning.

Appeal to Emotion

    Def.: Any attempt to change a person's view with information that appeals to his or her emotions (fear, pity, vanity, etc.) but which is logically irrelevant to the issue at hand. (Note: This is a version of Red Herring.)

    ID: Identify the emotion being appealed to and show why it is irrelevant to the issue at hand.

    MID:  There is nothing fallacious about employing information that tends to provoke strong emotional responses.  Appeal to emotion occurs only when such information is irrelevant to the issue at hand.

Appeal to Questionable Authority

    Def.: Accepting or recommending a claim on the basis of its appeal to an authoritative source of information when there are reasons for doubting the source in question. This may involve one or more of the following: (a) use of unnamed authorities, (b) use of authorities with a conflict of interest, (c) authorities switching fields.

    ID: Show that the reasoning relies only on an appeal to authority and give reasons for doubting the authority in question.

    MID:  (1) This fallacy arises only when a person has explicitly appealed to authority to support a conclusion.  If they have not used it, then to raise questions about their authority is to commit the fallacy of  ad hominem. (2) Don't turn your own ignorance into a criticism of the reasoning.  The author may cite authorities, or authoritative texts that you have never heard of.  This is not fallacious.  If you are going to criticize it, you need to produce reasons for thinking that the sources are questionable.

Appeal to Tradition or Common Opinion

    Def.: Accepting (rejecting) a claim on the basis of the fact that it is traditionally or commonly accepted (rejected) when there are good reasons for doubting the claim in question.

    ID: Show that the reasoning relies strictly on an appeal to tradition or common opinion and give he reasons for doubting the opinion or tradition at issue.

    MID:  This is a form of Appeal to Questionable Authority.  Same MID applies.

A Priorism

    Def.: Defending an empirical statement by systematically refusing to count anything as evidence against it.

    ID: Identify the statement in question and provide evidence that the speaker is refusing to count anything as evidence against it.

    MID:  A person who attempts to refute all evidence produced against a claim does not necessarily commit this fallacy. S/he must do so in a way that demonstrates that he is dismissing all evidence against the view without examining it.

Argument from Ignorance

    Def.: Defending a claim by appeal to the lack of evidence against it when reasonable efforts have not been made to find such evidence.

    ID: Show exactly how the lack of evidence against a view is being made to function as a reason in support of it. State your reason for doubting that reasonable efforts have been made to find such evidence.

    MID:  This fallacy does not consist simply in being ignorant of a subject or making a statement in ignorance of the evidence against it.  It requires the person to use the fact that there is no evidence against a view as a reason for believing the view.

Causal Determinism

    Def.: Asserting or denying a causal relationship based on the fact that the cause does not immediately, absolutely, or uniquely determine the effect.

    ID: Precisely identify the causal relationship being asserted and give reasons for thinking the speaker inappropriately assumes a deterministic model of causation .

    MID: Sometimes people do make strong deterministic statements.  E.g., some people appear to think that if you are exposed to a virus you are guaranteed to become infected by it.  In these cases it is obviously not fallacious to interpret their statements deterministically.


    Def.: Giving a reason for a conclusion that either presupposes the truth of the conclusion or simply restates the conclusion..

    ID: Identify the reason and the conclusion and show how the reason either presupposes or restates the conclusion.

    MID:  Simply restating a conclusion or stating the reason in different ways doesn't make the argument circular. You need to show that a statement that presupposes or merely restates the conclusion is functioning as a reason.


    Def.:  To be committed to the assertion of some statement S and  not-S at the same time.

    ID.:  Identify the statement being both asserted and denied.

    MID:  You must identify a single statement that is being both asserted and denied.  For example, it is not a contradiction to say "Most men are schmucks, but my Frankie is a sweetie pie,"  nor is it a contradiction to say "I love her when she's sweet to me, but I hate her when she's mean."

Distinction Without a Difference

    Def.: Drawing a conclusion on the assumption that different expressions mean significantly different things when they don't.

    ID: Identify the different expressions and show why they mean the same thing in the context in which they are used. Identify the conclusion that is affected.

    MID:  Sometimes distinctions are subtle but important.  For example "That's not a rabbit, that's a hare," may seem like a distinction without a difference, but they are actually different species that exhibit a variety of different behaviors.

Domino Fallacy

    Def.: Claiming that some event A will cause some remote event B by means of a chain of similar causes  the existence or reliability of which has not been established.

    ID: Precisely identify the causal relationship being asserted and give reasons for thinking it depends on a causal chain the existence of which has not been established.

    MID:  Domino effects are rare in nature, but they do occur. A flu epidemic is a good example.  If the reasoning provided gives adequate evidence that the requisite causal chain is in place, the fallacy does not occur.


    Def.: Drawing a conclusion on the assumption that two different uses of an expression  mean the same thing when they don't.

    ID: Identify the expressions, distinguish their meanings, and show how the author confuses them. Identify the conclusion that is affected.

    MID: People often uses the same word or expression in different ways without confusing their meanings.  For example:  "Butch is nuts about nuts" uses the word "nuts" in two different ways, but it doesn't confuse these meanings.

False Alternatives

    Def.: Misformulating a problem as a choice between two (or more) alternatives when there exist other alternatives that have not been considered.

    ID: Identify the alternatives in question and identify one or more important alternatives that have not been considered.

    MID:  It isn't sufficient simply to claim that there must be alternatives other than those considered.  You need to produce one that is at least as worthy of consideration as those being considered..

Gambler's Fallacy

    Def.: Arguing for a conclusion based on the assumption that the order or frequency with which a certain kind of chance event has occurred in the past affects the manner of its occurrence in the future.

    ID: Establish that the event in question is a chance event and show how the assumption in question is being  made.

    MID:  This fallacy does not consist simply in predicting the future on the basis of the past.  E.g. "I think Bob will probably leave for work at 6 AM tomorrow, because that when he usually leaves"

Genetic Fallacy

    Def.: Any reasoning formulated on the assumption that the circumstances under which something originated determines its current significance.

    ID: Identify what is being evaluated in terms of its origin and provide grounds for thinking that its current significance is not determined by these considerations.

    MID:  It is not fallacious to explain a phenomenon by reference to the circumstances under which it developed.  Normally the genetic fallacy consists in arguing that these circumstances determine (causally or morally) it's current significance.

Hasty Generalization

    Def.: Asserting a generalization (i.e, a principle)  without sufficient evidence.

    ID: Identify the generalization that is being established and give reasons for thinking the evidence is insufficient.

    MID:  Hasty Generalization is not simply jumping to a conclusion of any kind.  Be sure that the statement in question is a generalization.  Be sure that you do not misinterpret the statement as having the form "All X are Y," when the speaker is only asserting that  "Most X are Y" or "Some X are Y".


    Def.: Insinuating or suggesting a conclusion under conditions that suggest that one would be reluctant to claim it explicitly.

    ID: Identify the conclusion and explain why you regard it as an insinuation rather than a statement that the speaker would readily endorse.

    MID: This fallacy is not committed simply by failing to state a suggested conclusion explicitly.  You must have good contextual reasons for thinking (a) the speaker wanted the audience to draw the conclusion but (b) the speaker did not have or provide a basis for defending the conclusion explicitly.

Misuse of a Principle

    Def.: Applying a generally trustworthy principle to one of its known exceptions, often with the aim of refuting the principle itself.

    ID: Identify the principle, give reasons for thinking it is trustworthy, and give reasons for thinking that the fact in question is one of its known exceptions.

    MID: This fallacy consists in misusing the principle only in the manner described.  It does not, for example, consists in using a principle that makes no sense, or one that fails to connect a reason to a conclusion.

Neglecting a Common Cause

    Def.: Claiming that multiple events have distinct causes when the evidence suggests or is compatible with all the events having the same cause.

    ID: Precisely identify the multiple casual relationships being asserted and show how a single causal factor may account for all of the effects in question.

    MID:  It is not sufficient to claim that it is possible that a single factor accounts for all the effects.  You need to identify a plausible one.

Post Hoc

    Def.: Asserting that A is the cause of B just because B occurred after A.

    ID: Precisely identify the causal relationship being asserted and establish that the claim is based strictly on temporal order.

    MID:  Often people use the temporal order of events only as partial evidence for a causal connection.  The fallacy occurs when temporal order is the only (or by far the strongest) evidence provided.

Questionable Analogy

    Def.: Any reasoning based on the assumption that two or more things that are alike in one respect must be alike in some other respects when there are grounds for doubting this.

    ID: Identify the things being compared and identify a relevant difference between them that tends to undermine the conclusion being drawn.

    MID:  It is not sufficient simply to point out some difference between the things being compared.  There is always some difference.  Your task is to identify a relevant difference, i.e., one that gives reasons for doubting the legitimacy of the conclusion.

Red Herring

    Def.: Distracting attention from an issue by introducing an irrelevant issue or one that is only superficially related.

    ID: Identify the original issue and show why the issue introduced is irrelevant to it.

    MID: Be sure that you have identified the issue at hand accurately and that the new issue (a) really is irrelevant to the issue at hand and (b) is introduced in such a way as to distract attention from the original issue.

Reversing Cause and Effect

    Def.: Claiming that A is the cause of B when the evidence suggests or is compatible with B being the cause of A.

    ID: Precisely identify the causal relationship being asserted and give reasons for thinking that, given current evidence, the reverse relationship is at least as plausible as the one asserted.

    MID:  Be sure not to commit the fallacy of False Alternatives here.  Sometimes A causes B and B causes A.  In these cases a person can commits the fallacy only  if his reasoning depends on an ignorance of one of these relationships.

Slippery Slope

    Def.: Claiming that some inference A leads to some conclusion B through a chain of similar inferences which have not been adequately established.

    ID: Identify the original inference and the series of such inferences to which one is supposedly committed. Give reasons for doubting the chain of inferences in question.

    MID:  As with domino reasoning, not all slippery slope reasoning is fallacious.  Be sure that you have produced substantial reasons for doubting the chain of inference in question.

Straw Person

    Def.: Attempting to discredit a view by criticizing a weak version of the view or the reasoning given in support of it.

    ID: Identify both the original view and the weak version of that view and explain why the weak version is weak.

    MID: Make sure that what you identify as a weak version of a view really is being substituted for a stronger version.. This fallacy does not consist in simply adopting or criticizing what you regard to be a weakly formulated view.