Proof by example (also known as inappropriate generalisation) is a logical fallacy whereby one or more examples are claimed as "proof" for a more general statement. It has been suggested that this article or section be merged into Fallacy. ...

This fallacy has the following argument form: In logic, the argument form or test form of an argument results from replacing the different words, or sentences, that make up the argument with letters, along the lines of algebra; the letters represent logical variables. ...

I know that x X has the property P.

Therefore, all other elements of X have the property P.

The following example demonstrates why this is a logical fallacy:

I've seen a person shoot someone.

Therefore, all people are murderers.

That argument is obviously bad, but arguments of the same form can sometimes seem superficially convincing, as in the following example:

I've seen John's brother steal something.

Therefore, all John's family are thieves.

See also

• Modus ponens
• Affirming the consequent