For this sentence 本日は晴天なりといったとする, could I replace なり to です, if not, why?

Question

ChatGPT said '"なり" (nari) functions as a copula, which is a word that links the subject of a sentence with a predicate or description. Specifically, "なり" serves as a literary or formal version of the copula "だ" (da) or "です" (desu) in Japanese.' Is this correct or not in this sentence?

Answer 1

It's very misleading to say なり is a literary or formal version of だ. It is an obsolete copula that is no longer actively used in Japanese. You'll never come across it in contemporary Japanese, but you may find it if you try to read old documents on display in a museum written by samurai.

However, 本日は晴天なり is one of the rare exceptions where you might encounter なり in modern Japan. This phrase is widely known as a set phrase used to check microphones or radio transmissions. An English equivalent would be "Mic check one two", "Radio check" or Harvard sentences. Since 本日は晴天なり is more of a "test code" rather than an actual message, changing it, such as replacing なり with です, would defeat the main purpose of the phrase. You must always use this phrase verbatim, even if it's heavily snowing outside.

(By the way, while you don't need なり to read modern texts, you do need である, which is a formal and literary version of だ.)