Fowler calls for nor when you’re using this now-archaic style and want to join two negated verbs. For his example, he negates both verbs in the sentence He moves and speaks like this: He moves not, nor speaks. It’s only when you’re using the now-standard negation with an auxiliary verb, according to Fowler, that you should use or instead of nor. So in the more-modern phrasing, He moves not, nor speaks would be He does not move or speak. Fowler’s reasoning is that the not attaches to the auxiliary does, and therefore applies to both verbs in the same way as the auxiliary verb does.
How to Use Neither . . . Nor
Of course, nor is perfectly standard when it’s part of the correlative conjunction pair neither … nor. Then it can join just about anything. So when Severus Snape tells Harry Potter, “You are neither special nor important,” using neither … nor to join two adjectives is fine. However, if Snape had said, “You are not special nor important,” that would be a bit old-fashioned. The more modern way would be, “You are not special or important.”
How Not Can Be a Coordinating Conjunction
While we’re on the subject of negative coordinators, here’s a coordinator that gets completely left out of the FANBOYS mnemonic: not. Traditional grammars classify not as an adverb, which it certainly is in phrases such as did not check his answers. But it acts a lot more like a coordinator in sentences like We want jobs, not handouts! and Do it later, not now. It’s joining two items, in these examples nouns and adverbs, and comes between them instead of somewhere else.
This exclusion shows once again that parts of speech are not always clear cut, especially for function words like conjunctions, prepositions, and determiners. Mnemonics such as FANBOYS can help you memorize the most common members of some set, but don’t take them as the final word on what’s in and what’s out. Not every member these lists include is universally agreed on, nor do they capture every possible member of a set.