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It's interesting that the numbers 4 and 7 are often read using with kunyomi (よん, なな), even in many cases where the other numbers (1,2,3,5,6,8,9,10) would be read with onyomi.

For example, 34 is read さんじゅうよん (though さんじゅうし is another acceptable variant, I think?), but 35 would never be read さんじゅういつ.

What is the reason behind the use of よん/なな instead of し/しち ? That is, is there any historical or etymological reason, and why does this phenomenon only happen with 4 and 7 and not the other numbers?

One often cited reason (for 4) is that し is also the pronunciation of 死 (death). But this doesn't seem convincing, since し is a widely used sound in Japanese, and the meaning should be clear from context. Besides, し is used as a reading for 四, it's just that よん is also used.

Closely related is this question, but that is mainly about usage and does not cover the history and origin of this practice.

Aqualone
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    I cannot answer definitively, however, have you looked up the other meanings for し and しち, both have meanings pertaining to death. So, not very auspicious words. – A.Ellett Jan 22 '24 at 23:27
  • @A.Ellett The linked question covers this a bit, but not in detail enough for a definitive answer, so this might actually be useful (unless I missed another question somewhere). – cmw Jan 23 '24 at 01:02
  • It's also interesting that 九 as a standalone number is pronounced in its 漢 reading (きゅう), not in the older 呉 reading (く) like all the other numbers, including し and しち. The 呉 readings remain in compounds like 四月, 七月 and 九月. – aguijonazo Jan 23 '24 at 01:18

1 Answers1

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Note: This is based on the linked discussion/article at the bottom (filtered by my own bias).

Short answer: よん and なな are preferred mostly for the ease of distinguishing these two words (i.e., し and しち are too similar) and perhaps also distinguishing しち and いち.

As for なな, (quoting the quoted in the first link), 俚言集覧 (compiled around 1800) has the following:

「数目に七ト四ト音呼近似にて誤り易きを以て、七をナナと呼也。七百、七十、七をナナ百、ナナ拾、ナナというなり

The preference for よん is relatively new, or more concretely, it became popular after the war. Some phrases retain し.

I think most people today read them as にじゅうよん or よんかこく (actually my IME does not render しかこく to 四カ国) although にじゅうよん does sound a bit clumsy. Also, older people tend to read 四十 as しじゅう while today よんじゅう would be more common.

Reading 四 as し should be hardly productive anymore. That is, if Japan signs a treaty involving four nations now, it would be called よんかこく条約 (if such a name is used at all).

The mentioned superstition about し/死 may have played a role too. Of course し is used as a reading, but trying to avoid it where possible and totally tabooing it are different things (For example, I guess #4 or #42 is very commonly avoided in hospitals. I'm less sure about other buildings.).

sundowner
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