Recognizing logical fallacies is important when evaluating claims and arguments. At the same time, it’s important to recognize when someone misidentifies or misapplies a fallacy. People can claim to knock down valid claims by saying they commit a fallacy, when actually there’s no fallacy.
Take the “slippery slope” fallacy. Some slopes really are slippery. You have to evaluate a claim that X will lead to Y by the specifics, not just the formal structure. A trivia quiz I recently saw offered something like this as a supposed example of the fallacy: “If I give you an extra day to complete the assignment, I’d have to give it to anyone else who asks.” The quiz’s author was probably thinking something like, “The teacher can give special favors to some students and not others, so it’s fallacious to make that claim.” That assumes that consistent and fair treatment count for nothing.
The “Mandela effect” is defined, according to one article, as “a situation in which a large mass of people believe an event occurred when it did not.” The case which gives the effect its name is widespread “false recollection that Nelson Mandela died in the 1980s, though he died much later. Another example is false memories of a non-existent movie called “Shazam” starring the actor Sinbad. The claim that Salieri killed Mozart would also count. Yet the first two examples in the article are misremembering the TV show Sex and the City as Sex in the City and misspelling the Berenstain Bears as the “Berenstein Bears.” By this measure, all the people who spell my name “McGrath” are an example of the Mandela effect. Writing “loose” when it’s supposed to be “lose” must be a Mandela effect too.
Misremembering small details doesn’t count as a mass delusion that something occurred. If lots of people thought that there was a distinct show called Sex in the City or a less-known set of kidlit characters called the Berenstein Bears, that might count as a Mandela effect, but small errors in phrasing and spelling aren’t mass delusions even if they’re widespread.
“Excluded middle” is a tricky one. The term is used in two opposite senses. The “fallacy of the excluded middle” may refer to claims of a middle ground between A and not-A. When a category is clearly specified, then everything where it’s a meaningful predicate has to fall under one or the other. A triangle is a right triangle, or it isn’t. A bill became law or it didn’t. But some predicates aren’t precise, and it isn’t always possible to say something falls under it or doesn’t. For example: “That building is tall.” “This car was badly designed.” There’s another “fallacy of the excluded middle” that refers to neatly categorizing everything as A or not-A when the criteria for A aren’t sufficiently clear. Either way, I suggest using other terminology instead of “excluded middle” to avoid confusion.
Late addition: “No true Scotsman” is a fallacy when it’s used to exclude people from a group they belong to, but saying someone doesn’t truly subscribe to a philosophy or religion is a different matter. For instance, someone might respond to antisemites in a church by saying, “No true Christian hates Jews.” That is, hatred of Jews is inconsistent with Christianity, so much so that it disqualifies a person from being counted as Christian. If you say this, you have to concede that a lot of people historically regarded as Christians weren’t “true Christians,” but as long as you’re willing to do this, there’s no contradiction in your position.
The term is often used metaphorically. If Trump says that all real Americans support his policy, he isn’t saying that opposing him makes a person a non-citizen. (Yet. Check back in a couple of months.) He’s saying that true Americanism consists unswerving loyalty to him, and his opponents are inferior Americans.
These uses are more common than actual instances of the “no true Scotsman” fallacy.
Recognize fallacies, but don’t apply them blindly.