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Logical Fallacies: Arguments, Reasoning, and the Fallacy

Fallacies are defects in an argument that cause it to be invalid, unsound, or weak. In a deductive argument, the existence of a fallacy means that the argument is not valid - even if the premises are true, the conclusion might still be false. A fallacy does not guarantee it is false; a fallacious argument fails to provide a good reason to believe the conclusion, even if that conclusion is correct.
  1. Critical Thinking

Stories of Past Gullibility: Tell Us About Beliefs or Ideas You Were …
Gullibility is a human trait and we've all been gullible about something at some point in our lives. We may even still be gullible about something now without realizing it. As you look back at your own past, can you identify beliefs, ideas, or claims which you were gullible about and which you wouldn't so easily accept now? Did you used to...

Fallacies of Ambiguity: The No True Scotsman Fallacy
What is 'The 'No True Scotsman...' Fallacy and how is this fallacy committed? This is actually a combination of several fallacies, but since it rests ultimately on shifting the meaning of terms - a form of equivocation - and begging the question, it receives special attention.

Fallacies of Presumption: Begging the Question (Petitio Principii)
Begging the Question is the most basic and classic example of a Fallacy of Presumption. Begging the Question presumes the conclusion which is at issue in the first place. This can also be known as a 'Circular Argument' because the conclusion essentially appears both at the beginning and the end of the argument, it creates an endless circle,...

Fallacies of Relevance: Appeal to Authority Overview and Introduction
Appeal to Authority: A fundamental reason why the Appeal to Authority can be a fallacy is that a proposition can be well supported only by facts and logically valid inferences. But by using an authority, the argument is relying upon testimony, not facts. A testimony is not an argument and it is not a fact.

Appeal to Authority: Argumentum ad Populum (Appeal to Numbers)
Appeal to Numbers This fallacy occurs any time the sheer numbers of people who agree to something is used as a reason to get you to agree to it and takes the general form: When most people agree on a claim about subject S, the claim is true (normally an unstated premise). Claim X is one which most people agree on. Therefore, X is true.

Fallacies of Relevance: Appeal to Tradition
Appeal to Tradition: This form of the Appeal to Authority is slightly different from the others in that it does not directly make an appeal to the authority of any particular people. Instead, it makes its appeal to the authority of the collective interests and habits of people, as expressed in tradition or culture.

What is a Fallacy? Understanding Defective Arguments
Fallacies are defects in an argument that cause an argument to be invalid, unsound or weak. Fallacies can be separated into two general groups: formal and informal. A formal fallacy is a defect which can be identified merely be looking at the logical structure of an argument. Informal fallacies are defects which can be identified only through an...

Fallacies of Presumption: False Dilemma, Excluded Middle, False Dichotomy,...
The False Dilemma fallacy occurs when an argument offers a false range of choices and requires that you pick one of them. The range is false because there may be other, unstated choices which would only serve to undermine the original argument. If you concede to pick one of those choices, you accept the premise that those choices are indeed the...

What is a Fallacy?
Fallacies can be separated into two general groups: formal and informal. A formal fallacy is a defect which can be identified merely be looking at the logical structure of an argument rather than any specific statements.

Logical Fallacies: Alphabetical Index
Alphabetical list of all of the fallacies, formal and informal, which are cataloged and explained on this site. More are added regularly, so keep checking back over time.

Fallacies of Grammatical Analogy
Arguments with this sort of defect have a structure which is grammaticaly close to arguments which are valid and make no fallacies. Because of this close similarity, a reader can be distracted into thinking that a bad argument is actually valid.

Fallacies of Ambiguity
With these fallacies, some sort of ambiguity is introduced either in the premises or in the conclusion itself. This way, an apparently false idea can be made to appear true so long as the reader does not notice the problematic definitions.

Fallacies of Relevance
Fallacies in this category have in common the characteristic that they all make use of premises which are logically irrelevant to the final conclusion. However, this is not usually noticed because these same premises are often relevant for psychological reasons, thus making the conclusion seem to follow.

Fallacies of Presumption
Fallacies of presumption are created when the premises of the argument presume something illegitimately. Sometimes what is presumed is the actual conclusion itself; however, it is also possible to presume some other important or related issues. In general, these are problems because if the assumptions were made explicit, they would provide grounds for questioning the conclusion.

Fallacy of Amphiboly
The fallacy of amphiboly occurs when a sentence is ambiguous because the grammar allows for multiple interpretations.

Fallacy of Accent
The fallacy of accent occurs when the meaning of a word or sentence is ambiguous and dependent on where the spoken stress is placed.

Fallacy of Equivocation - Equivocation Fallacy Due to Multiple Definitions
The Fallacy of Equivocation occurs when a term is used with two or more meanings in the same argument.

Illicit Observation Fallacy from Contraries & Contradictories
The fallacy of Illicit Observation occurs if two terms in an argument are used as if they were negations or opposites of each other when they really aren't.

Quoting out of Context Fallacy
Quoting out of context becomes a fallacy when someone selectively quotes a passage that distorts, alters, or even reverses the originally intended meaning.

Scope Fallacy
The scope fallacy is created by ambiguities in grammar - specifically, the 'scope' of grammatical / logical operators like 'not'. A scope fallacy can be difficult to recognize but it can introduce significant problems in an argument.

Quantifier Fallacy - Shifting Quantifiers Over the Course of an Argument
Quantifier Fallacies are a type of Scope Fallacy and occur when scope quantifiers like 'some' and 'every' shift over the course of the argument.

Reification / Hypostatization Fallacy - Ascribing Reality to Abstractions
Reification, also sometimes known as Hypostatization, is a fallacy of ambiguity that occurs when a person treats an abstract concept of mental construct as if it had real, concrete existence. This frequently occurs when metaphors are taken too far or are treated too literally.

Abusive ad hominem Fallacy - Insulting a Person to Dismiss their Arguments
The abusive ad hominem is the most easily recognized ad hominem fallacy. It occurs whenever someone uses personal attacks as a justification for rejecting someone else's conclusions. It's only a fallacy, though, when it goes beyond just the personal attack - mere insults are not a fallacy.

Tu Quoque Fallacy - Ad Hominem Fallacy That You Did It Too!
The logical fallacy 'tu quoque' occurs whenever one tries to justify what they've said or done by insisting that another person has done the same thing.

Fallacies of Ambiguity Index
Fallacies of ambiguity occur whenever some aspect of language, grammar, or definition is ambiguous rather than defined clearly - usually in an argument's premises or conclusion.

Poisoning the Well Fallacy - Fallacy of Preemptively Making a Person Look Bad
Poisoning the well is a fallacy that people commit when they try to undermine confidence in an argument before the argument is made by casting doubt on the morality of the people making the arguments.

Circumstantial ad hominem Fallacy
Dismissing an argument by pointing to the circumstances surrounding it, like the identity of those who believe it, is known as the circumstantial ad hominem fallacy.

Genetic Fallacy - Dismissing an Argument Based on Where it Originated
The Genetic Fallacy is a type of ad hominem fallacy which occurs when one dismisses an argument based on where or with whom it originated.

Argument Against the Person - Argumentum ad hominem
This fallacy occurs whenever someone tries to rebut an argument by focusing on the person making the argument rather than on the qualities of the argument itself.

Appeal to Poverty / Appeal to Money - Fallacy of Appealing to Money or Wealth
It's a fallacy to argue that a person's wealth or poverty is relevant to believing what they claim. It's also a fallacy to argue that the cost of an item is relevant to how good it is.

Appeal to Age - Fallacy of Appealing to Age, Tradition, or Custom
The Appeal to Age fallacy occurs when one argues that the when something is old, then this somehow enhances the value or truth of the proposition in question.

Appeal to Novelty - Fallacy of Appealing to Newness
The Appeal to Novelty, also known as the argumentum ad novitatem, occurs whenever someone attempts to base a conclusion on how new, recent or 'fresh' something is. Sometimes it is phrased as an attack on something as being too old-fashioned, thus implying that a newer alternative is better.

Appeal to Force/Fear - Argumentum ad Baculum
The Appeal to Force or Fear, also known as the argumentum ad baculum, occurs whenever someone makes an implicit or explicit threat in order to get you to accept their conclusion. Sometimes the threat might be one of violence but it can also be a threat against your happiness or well-being generally.

Appeal Flattery - Logical Fallacy
The Appeal to Flattery fallacy occurs when a person compliments or flatters to get someone to accept the truth of a proposition.

Appeal to Pity (Argumentum ad Misercordiam) Logical Fallacy
The Appeal to Pity fallacy is an attempt to get people to agree with a conclusion by evoking pity and sympathy either with their situation or with the situation of some third party.

Logical Fallacy Composition
The Fallacy of Composition involves taking attributes of part of an object or class and applying them to the entire object or class.

Logical Fallacy Division
The Fallacy of Division involves someone taking an attribute of a whole or a class and assuming that it must also necessarily be true of each part or member. It is similar to the Fallacy of Composition, but in reverse.

Fallacy Appeals Emotion Desire
Arguments that try to elicit an emotional reaction from people and then use that reaction to get them to agree to the conclusion commit the fallacy of an Appeal to Emotion.

Complex Question Fallacy
The Complex Question fallacy occurs when an argument depends upon hidden premises that aren't defended or explained.

Suppressed Evidence Fallacy
When true and relevant information is left out for any reason, the fallacy called Suppressed Evidence is committed.

Oversimplification Exaggeration Fallacy
The causation fallacy known as oversimplification and exaggeration occurs whenever the series of actual causes for an event are either reduced or multiplied to the point where there is no longer a genuine, causal connection between the alleged causes and the actual effect.

Correlation vs. Causation Fallacies
Just because two events correlate (are close in time or space) does not mean that one has caused the other. The Latin term for such an error is called "non causa pro causa," which means "non-cause for the cause." It is important to try and break ourselves of this habit and become more critical of our natural inclinations in such cases.

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