Yo no naka wa nani ka tsune naru asukagawa kinō no fuchi zo kyō wa se ni naru - Kokin Wakashu(English Translation & Meaning)

世の中は何か常なるあすか川
昨日の淵ぞ今日は瀬になる

Roma-ji: Yo no naka wa nani ka tsune naru asukagawa kinō no fuchi zo kyō wa se ni naru
English Translation: In this world of ours
what is there that ever stays?
Asuka River:
the deep pool of yesterday
today becomes the shallows.
Meaning: In this world, what is there that stays the same? In the Asuka River, the place that was a deep pool only yesterday has become shallow rapids today.
Commentary: Book Eighteen Miscellaneous Poems II 933

Headnote: "Topic unknown"
This is the opening poem of Book Eighteen, Miscellaneous Poems II, of the Kokin Wakashū. Through the shifting pools and shallows of the Asuka River, it sings of impermanence: nothing in this world endures. By showing the river changing between yesterday and today, it gives a vivid image of how unsettled human life is.
The line "yesterday's deep pool becomes today's shallows" gave rise to the phrase "the pools and shallows of the Asuka River," long used to describe the violent changes of the world.
Placing a poem on impermanence at the head of the book, the compilers follow it with poems lamenting the sorrows of the world. Ise's poem 990 in this book builds on these pools and shallows to speak of selling her house, and the closing poem, 1000, also sings of a mountain stream, so that the beginning and end of the book answer each other through river imagery.
The author is recorded as anonymous, and the name has not come down to us.

The first line, "In this world," sets out human life and society as the theme. Many poems in this book, such as 941, 942, 948 and 987, open with "the world," and this opening line raises the theme of the whole book.
The second line, "what is there that ever stays?", is a rhetorical question meaning that nothing is constant. The poem breaks after this line and moves to a concrete scene.
The third line names the Asuka River in Yamato, known for its shifting course. The "asu" in the river's name echoes asu, "tomorrow," and sits alongside "yesterday" in the fourth line and "today" in the fifth.
The fourth line, "the deep pool of yesterday," refers to the spot that was deep water until yesterday. The emphatic particle zo here governs the attributive ending of naru in the last line.
The last line, "today becomes the shallows," completes the contrast between pool and shallows, showing how drastic the change can be within a single day.
Author: Unknown Poet
Source: Kokin Wakashu
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