Time to put out another fallacy collection; my goal is to include all major fallacies in this upcoming book. Here is my write up of the Appeal to Purity Fallacy; also known as the No True Scotsman fallacy.
This fallacy occurs when there is an attempt to protect a generalization about a group from a counterexample by changing the definition of the group in an unprincipled way to exclude the counterexample. This is a fallacy because the tactic does not refute the counterexample, but merely it asserts does not apply. The fallacy is also known as the No True Scotsman fallacy thanks to the philosopher Anthony Flew. The fallacy has the following form:
Premise 1: Counterexample E has been made against Claim C about group G.
Premise 2: Counterexample E does not apply to any true member of group G.
Conclusion: C is true (and E is false).
Like many fallacies, it draws its persuasive power primarily from psychological factors. A member of the group in question or someone who has a favorable view of the group would have a psychological, but not logical, reason to reject the counterexample. Few are willing to believe negative things about groups they like or identify with. In Flew’s example, a Scotsman refuses to believe a story about the bad behavior of other Scotsmen on the grounds that no true Scotsman would do such things. People can also reject such a counterexample on pragmatic grounds, such as when doing so would provide a political advantage.
The fallacy can also be used in the opposite way—to reject positive counterexamples about negative claims. For example, if someone claims that all video games are senselessly violent and rejects counterexamples of non-violent video games, then they are committing this fallacy. This variation is also fueled by psychological factors, in this case negative ones: a person dislikes the group in question and hence is motivated to reject positive counterexamples against negative claims. This can also be done for pragmatic reasons; for example, a politician might refuse counterexamples that go against their negative rhetoric about a group they are trying to demonize.
The main defense against this fallacy is to consider whether a counterexample is being rejected on principled grounds or is being rejected without evidence, such as on psychological or pragmatic grounds. One way to try to overcome a psychological bias is to ask what evidence exists to reject the counterexample. If there is no such evidence, then all that would be left are psychological or pragmatic reasons—which have no logical weight.
Sorting out who or what belongs in a group can be a matter of substantial debate. For example, when members of religious groups do awful things the question often arises as to whether these people are true members of these religious groups. For example, the Westboro Baptist Church is infamous for its slogan “God Hates Fags” and hate speech against a wide range of people. Some might contend that they are not true Christians because their beliefs seem counter to the claimed core values of Christianity, while others assert that they are Christians because they claim to be and back up their views with scripture. Debates over group membership need not be fallacious—if a person claims that true Christians do not hate LGBT people and rejects the counterexample of the Westboro Baptist Church by providing reasons why they do not meet the proper definition of “Christian”, then this fallacy has not been committed. This is because they have provided reasons to support their claim rather than simply rejecting the counterexample out of hand. Providing a guide to settling such disputes goes far beyond the scope of this work, but the above fallacy is not a tool that should be used in rational efforts to address such matters.
While it is an error to dismiss counterexamples out of hand, it is also an error to simply accept that what is claimed about some members of a group applies to all or most members of a group. For example, someone might note that a migrant committed a crime and then assert that most migrants are criminals. As another example, one might assert that most police officers are prone to excessive violence because some have been involved in high profile cases of police violence. These would be example of the Hasty Generalization fallacy—leaping to a conclusion too quickly from a sample that is too small to support it properly.
Bill: “Islam is a religion of peace. No Muslim would harm another person.”
Sally: “What about the Muslims who are fighting in Syria and Yemen right now?”
Bill: “They are not true Muslims.”
Bill: “Christianity is a religion of peace. No Christian would harm another person.”
Sally: “What about all the Christians that killed each other in the world wars and other conflicts?”
Bill: “They were not true Christians.”
Mark: “Republicans are not racists and certainly not white supremacists.”
Hector: “What about those racists and white supremacists who support Republican politicians?”
Mark: “We don’t accept them in our party; we are not racists.”
Mark: “Democrats are not sexists; we are all for equal rights and respect women!”
Hector: “So, what about those Democrats who got outed by #MeToo for assaulting women?”
Mark: “They are obviously not real Democrats; no real liberal would do such things!”