Why do sentences with いわんや often end with をや?

Question

I was reading about the (apparently) archaic-sounding 況んや{いわんや}, which is used like まして, but getting to the examples sentences I see many ending in をや/においてをや:

私は貧乏でなかなか人並みの生活もできない, いわんや貯蓄をやだ.

The best entries I found for just をや came from 現代国語例解辞典第五版 and 新明解国語辞典第八版 respectively:

「いはんや悪人においてをや」のような、「いわんや…においてをや」の形で、前文の事柄が成立するのだから、後文の事柄が成立するのは当然のことであることを示す。まして…は言うまでもない。
㊂〔終助詞「を」＋副助詞「や」〕比較的程度の軽い前件と対比して、後件は問題無く成立することを表わす。「善人なほも（ち）て往生を遂ぐ、況(イハンヤ)悪人━」

I don't feel that either of these explanations describe what をや is actually doing in these sentences, considering I'd assume いわんや is doing most of the work here. You don't add something like this to まして sentences I believe. Even if this is just the normal object marker and exclamatory や, it just seems rather strange why this is a pattern to me. Is there any reason it is used like this with いわんや?

Answer 1

This expression originated from the kanbun-kundoku tradition. "いわんや～をや" is a pattern Japanese high school students are supposed to learn along with "～するあたわず" or "～をして～しむ" in kanbun classes.

Originally, 況Ａ乎 in kanbun was simply read as "Ａを言わんや (Will I mention/describe A?)". Here, を marks the object of 言う, ん is a volition marker, and や is a question particle rather than an exclamation particle. Then the word order was artificially inverted to conform to the SVO word order of Chinese, resulting in the reading "いわんやＡをや". At this point, いわんや started to function like an adverb. Later, this construction with a peculiar word order became established outside kanbun contexts as an elevated way of saying "not to mention A".

いわんや貯蓄をや。
→ 言おうか、貯蓄(のこと)を。

would I (even/also) mention savings?
→ not to mention savings / let alone savings

をや might seem redundant if you think of いわんや as "let alone", but in Japanese, certain adverbs very commonly correspond to specific expressions (もし～なら, まるで～ようだ, よもや～まい). I don't think this pattern is exceptional in this regard.

That said, using いわんや～をや in an ordinary Japanese text is almost like suddenly mixing barely understandable Latin into English text. Most people should not use this construction in daily life, and it's more than enough if you can understand its meaning.