Q: What noun can only be correctly used in the singular, according to the first edition of Henry Fowler's famous book "Modern English Usage"?
A: "Protagonist". In classical Greek plays, the protagonist was by definition the single most important character - indeed, "protos" means "first" in Greek, and "agonistes" means "actor". In the 1926 edition of "Modern English Usage", Fowler claimed that it was therefore erroneous to speak of the "protagonists" of a drama or work of fiction - the protagonist could only be the most important character. This was hugely controversial, and is by now largely disregarded.
Source: Simon Winchester, The Professor and the Madman: A Tale of Murder, Insanity, and the Making of the Oxford English Dictionary, HarperCollins, 1998.
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