Negation in 未然形 + む(ん)

Question

This question has been inspired by this Q&A, from which I learned about 未然形 + む(ん)'s various functions. I noticed two lines on the reference page @naruto points to under 推量, both seemingly sharing the same 未然形 + む(ん) structure. However, the first one is glossed as negative, while the second one translates in modern Japanese as a positive sentence.

推量…［～う・～だろう］

懈怠の心あることを知らんや。（徒然草・九二段）
　（怠けた心が生じることを知らないだろうか。）

夕には朝あらんことを思ひ、朝には夕あらんことを思ひて（徒然草・九二段）
　（夕方には明日の朝があるだろうと思い、朝には夕方があるだろうと思って）

Is there a reason for this? Or is this a mistake on the site editor's part?

Answer 1

The first example has 知らんや. It's important to note the ending particle や -- this is used in Classical Japanese after a suppositional ～む ending to indicate a rhetorical question with an implied negative outcome, a bit like English construction "would he know that?" → implying that he wouldn't.

The あらん examples with ～ん (from older suppositional ～む) are not followed by this same negative-rhetorical particle, so the translations into modern Japanese phrasing do not include any negative sense.

See also:

• This Q&A about the term [烏有]{いずくんぞあらんや}, which includes that same ～むや construction.
• The Kotobank entries for や, such as in Daijisen here, specifically sense 六.2.イ: 「2.文末用法。㋑反語を表す。…だろうか（いや、そうではない）。」