What type of clause is 「蛙飛び込む」 in the famous haiku by Basho?

Question

Usually, Basho's famous haiku, when written with a translation, is presented thus:

古池や
蛙飛び込む
水の音

And translated roughly (similar to three out of five translations available in Wikisource):

An old pond
A frog leaps
The sound of water

However, there are inversions of order of the last two lines, as was brought to my attention in a recent post I made in the Literature Stack Exchange:

An old pond
The sound of water
As a frog leaps in/Of a frog leaping in

Here, the second line is modified by the third, whereas in the first, they stand separate.

In Japanese, what type of clause is the phrase 「蛙飛び込む」 in this haiku?

Answer 1

Grammatically 蛙飛び込む modifies 水の音 as a relative clause. It's not that 水の音 modifies 蛙飛び込む. Japanese is an almost pure head-final language, which means a modifying part almost always comes before a modified part.

This relative clause is a bit special, and it's a bit hard to give a very literal translation of 蛙飛び込む水の音. This is called a gapless relative clause described here, or type C relative clause described here. Basically 蛙飛び込む explains what kind of 水の音 we are dealing with. One rather literal translation would be "the sound of water of/from a frog's leaping in." Although this one is grammatically closer to the original haiku, it doesn't look similar to the original in terms of line order. So neither is definitely better than the other.