No True Scotsman, or How to Adopt a Fallacy Before Admitting a Mistake

One of the most fascinating (and frustrating) aspects of political discourse is the sheer number of holes it tends to have. In debates about security and surveillance, the famous "nothing to hide" argument is truly tiresome, but politicians also love generalization. When they face overwhelming evidence that their generalization doesn't hold, they modify the original definition, appealing to factors like purity and identity. These cases are embodied by the fallacy of the false Scotsman, or simply the "No true Scotsman" fallacy.

The phrase dates back to 1971, when Professor Anthony Flew used it in "Introduction to Western Philosophy", but the most popular citation comes from his 1975 book, "Thinking About Thinking":

The passage describes a certain Hamish McDonald, a Scotsman, sitting while reading a copy of the Glasgow Morning Herald. In that newspaper he finds an article called "The Sexual Maniac of Brighton (England) Attacks Again". Horrified, Hamish openly declares that "no Scotsman would do such a thing". However, the next day he discovers that the Herald published an article about a man from Aberdeen (Scotland), whose appalling actions make the Brighton maniac look like a saint. The news proves Hamish was wrong, but instead of admitting it, Hamish changes his original statement, saying "no true Scotsman would do such a thing".

In essence, what Hamish is doing is denying that criminal's sense of belonging, since committing a crime is enough evidence to determine that he was not an "authentic Scotsman" in the first place. Of course, Hamish's reasoning is fallacious, because there is no premise in the definition of "Scotsman" that makes those brutal acts impossible or improbable. Under certain conditions, the fallacy is used as a form of retroactive disqualification, separating the action and the individual from the group ("if you do that, it's because you were never one of us from the start!").

The fallacy is very common in religious spaces. How many times have we heard about "true Christians", "true Muslims" or "true Jews"? An appeal to purity as a way to protect oneself from the possibility of being wrong.

When it comes to exceptions, everything depends on the quality of the original definition and its consistent application. A frequent example falls into the expression "no true vegetarian would eat a pork steak"; The fallacy does not apply because the action of consuming the steak would invalidate the vegetarian condition.