Fallacy of the Week Promoting Rationality

Fallacy of the Week

Because I said So = Truth?

Context: Dr. Oz, a popular television host and doctor, is under fire for some of the claims he made as part of his television show. Most recently, a group of University doctors have requested that Columbia University fire Dr. Oz via a written letter that claims: “Dr. Oz has repeatedly shown disdain for science and […]

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Arguments can sometime be confusing because they contain ambiguous words or phrases whose meanings shift and change throughout the argument. Often when reasons only appear to support the conclusion, this is due to ambiguity. Vagueness or manipulation in language can cause an argument to become a fallacy of ambiguity. We often do not notice subtle manipulations in language and are therefore mislead to believe the argument.
To determine if an argument is an Ambiguity Fallacy, ask yourself:

  • Is something unclear?

  • Are words or phrases being used differently throughout the argument?

Ambiguity Fallacy Types


This fallacy occurs when an argument purposefully changes the meaning of a word or phrase in order to conceal the reasonableness of the conclusion.
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Straw Man

This fallacy occurs when an argument misrepresents an idea so that it is easier to challenge.
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In order for an argument to be true, the reasons have to directly support the conclusion. When the reasons are not connected to the conclusion, and are therefore irrelevant to the truth of the conclusion, the argument becomes a fallacy of relevancy. Often these reasons are true but have nothing to do with the position being argued. We often tend to find these types of fallacious arguments convincing because the reasons are reasonable and perhaps not obviously irrelevant. To determine if an argument is a Relevancy Fallacy, ask yourself:

  • Is something irrelevant within the argument?

  • Do the reasons have anything to do with the conclusion?

Relevancy Fallacy Types


Personal Attack

This type of fallacy attempts to distract the audience from the argument by placing the focus on a flaw in the person’s character that is irrelevant to the topic being discussed.
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Appeal to Authority

This fallacy occurs when an argument uses the authority of a non-expert as a reason to support the conclusion.
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Appeal to Emotion

This fallacy occurs when an argument relies on manipulating feelings in order to make a conclusion convincing.
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Appeal to Popularity

This fallacy uses a popular belief as the only support for a particular idea. It is essentially a form of peer pressure.
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Hasty Generalization

This fallacy occurs when a generalization is made without sufficient evidence or support because the example is either too rare, too specific, or not truly representative of the larger picture.
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Non Sequitur

This type of fallacy occurs when the conclusion does not logically follow from the premises. That is, the reasons are irrelevant to the conclusion.
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Assumptions are thoughts or beliefs that we believe to be true even though they have not properly be tested and verified as true. Since assumptions are a part of our everyday lives, we often do not notice when they are used in arguments. When an argument is assuming something to be true that is not necessarily true in order to establish a particular conclusion, the argument becomes a fallacy of presumption. If an argument is based on false reasons, then we cannot guarantee that the conclusion is true.
To determine if an argument is a Presumption Fallacy, ask yourself:

  • Is something being assumed?

  • Are reasons one of claiming something as fact when it really should?

Presumption Fallacy Types

Begging the Question

This fallacy is a type of circular reasoning that hides the conclusion in one of the reasons. This type of fallacy is not reasonable because it serves to only prove what is already assumed.
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This type of fallacy often confuses correlation as causation by making the claim that because two things happen together one must be the cause of the other.
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Slippery Slope

This type of fallacy assumes that if one thing happens, something else will necessarily happen even if this is not necessarily the case.
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