In Classical Greece, philosophers and rhetoricians classified dishonest or erroneous arguments by identified types. Many are known nowadays by their Latin names, such as "ad Hominem", "Argumentum ad Ignorantiam" (Argument from Ignorance), "Post Hoc Ergo Proctor Hoc", etc.
This process of identifying and codifying logical fallacies enables people to recognize when an opponent in a debate, or a public speaker, a writer, an acquaintance, etc., uses a dishonest or erroneous argument in attempt to convince from a weak or failed position.
These false arguments are known as "logical fallacies". The word "logical" means "having to do with logic" or "constructed according to logic". The word "logic" implies a rigorous application of rational thought, following the formal structures of rational thought. A "fallacy" is a false or erroneous claim. "The moon is made of green cheese" is a fallacious statement--it is a statement of fact that is untrue. A logical fallacy is a fallacy that is not false (or not only false) because there is a factual incorrectness, but that is false because the reasoning behind it is false. "Jim's uncle Joe went to prison, so Jim would not be a good mayor" is an example of the logical fallacy known as an "ad Hominem" argument.
The "No True Scotsman" fallacy is an attempt to dismiss a countering argument by claiming that by the fact of its presenting a countering example, the argument belongs to a different category. The example is this:
A Scot sees in the news that a violent criminal is loose in Brighton, in England. He sneers at it, saying that no Scot would do such things. Then the news moves on to an even worse criminal in Aberdeen, in Scotland. The Scot then dismisses the criminal in Aberdeen, by saying that "no true Scotsman would do that."
So here is an example:
- "Americans love baseball!"
- "Chris does not like baseball."
- "Hmpff. Then Chris is not a true American."