Intentionally blank page paradox

Intentionally blank page: Many documents contain pages on which the text "This page is intentionally left blank" is printed, thereby making the page not blank.

Is-Ought

The is-ought fallacy occurs when a conclusion expressing what ought to be so is inferred from premises expressing only what is so, in which it is supposed that no implicit or explicit ought-premises are need. There is controversy in the philosophical literature regarding whether this type of inference is always fallacious.

Example:

He's torturing the cat.
So, he shouldn't do that.

This argument clearly would not commit the fallacy if there were an implicit premise indicating that he is a person and persons shouldn't torture other beings.

Irrelevant Reason

This fallacy is a kind of non sequitur in which the premises are wholly irrelevant to drawing the conclusion.

Example:

Lao Tze Beer is the top selling beer in Thailand. So, it will be the best beer for Canadians.

Irrelevant Conclusion

If an arguer argues for a certain conclusion while falsely believing or suggesting that a different conclusion is established, one for which the first conclusion is irrelevant, then the arguer commits the fallacy of irrelevant conclusion.
Example:

In court, Thompson testifies that the defendant is a honorable person, who wouldn't harm a flea. The defense attorney rises to say that Thompson's testimony shows his client was not near the murder scene.

The testimony of Thompson may be relevant to a request for leniency, but it is irrelevant to any claim about the defendant not being near the murder scene.

Invalid Reasoning

An invalid inference. An argument can be assessed by deductive standards to see if the conclusion would have to be true if the premises were to be true. If the argument cannot meet this standard, it is invalid. An argument is invalid only if it is not an instance of any valid argument form. The fallacy of invalid reasoning is a formal fallacy.

Example:

If it's raining, then there are clouds in the sky. It's not raining. Therefore, there are no clouds in the sky.

This invalid argument is an instance of denying the antecedent. Any invalid inference that is also inductively very weak is a non sequitur.

Intensional

The mistake of treating different descriptions or names of the same object as equivalent even in those contexts in which the differences between them matter. Reporting someone's beliefs or assertions or making claims about necessity or possibility can be such contexts. In these contexts, replacing a description with another that refers: the same object is not valid and may turn a true sentence into a false one.

Example:

Michelle said she wants to meet her new neighbor Stalnaker tonight. But I happen to know Stalnaker is a spy for North Korea, so Michelle said she wants to meet a spy for North Korea tonight.

Michelle said no such thing. The faulty reasoner illegitimately assumed that what is true of a person under one description will remain true when said of that person under a second description even in this context of indirect quotation. What was true of the person when described as “her new neighbor Stalnaker” is that Michelle said she wants to meet him, but it wasn’t legitimate for me to assume this is true of the same person when he is described as “a spy for North Korea.” Extensional contexts are those in which it is legitimate to substitute equals for equals with no worry. But any context in which this substitution of co-referring terms is illegitimate is called an intensional context. Intensional contexts are produced by quotation, modality, and intentionality (propositional attitudes). Intensionality is failure of extensionality, thus the name “intensional fallacy”.

Inconsistency

The fallacy occurs when we accept an inconsistent set of claims, that is, when we accept a claim that logically conflicts with other claims we hold.

Example:

I'm not racist. Some of my best friends are white. But I just don't think that white women love their babies as much as our women do.

That last remark implies the speaker is a racist, although the speaker doesn't notice the inconsistency.

Incomplete Evidence

See Suppressed Evidence.

Ignoring a Common Cause

See Common Cause.

Ignoratio Elenchi

See Irrelevant Conclusion.