The joy of life in the valley, having left the world,
is the call of an uguisu lingering in its nest

世を出でて溪に住みけるうれしさは古巣に残る鶯のこゑ

One of the challenges of Japanese poetry is that it is all so interconnected, and yet each piece is so small, that the authenticity of your pleasure is often in doubt. What I mean by "authenticity" here is fuzzy; perhaps the extent to which what you get out of the poem matches what the author intentionally put in, or the degree to which your enjoyment of the poem conforms to that of a hypothetical super-scholar with perfect understanding (and recall) of the entire history of Japanese literature, history, orthography, and so on. Of course, both of these are ultimately unknowable things: we can never know exactly what authors meant, and no-one can know everything. The reality is that we are all lost in the woods, but some of us have better tracking skills than others.

I came across the poem at the start of this post reading the Iwanami Bunko edition of Saigyō's Sanka shū 山家集 ("Poems of a Mountain Home," as Burton Watson has it), edited by Sasaki Nobutsuna 佐々木信綱. It caught my attention because it used 溪 for tani, "valley," instead of the more common 谷.

In Chinese, as I understand it, these two characters have separate meanings: 溪 is a mountain stream or creek, while 谷 is a valley, water optional. But in modern Japanese dictionaries, 溪 is usually given as an alternate way to write 谷 in the sense of tani, a native Japanese word that doesn't distinguish between the senses described above. At best, 溪 will have its own entry under the Sino-Japanese pronunciation kei, glossed as "谷、谷川" ("valley, valley stream").

So 溪 is much less frequent in Japanese writing than 谷, and when it does appear it is usually as part of a Sinitic vocabulary item (e.g. keikoku 渓谷, i.e. "渓 and 谷," which is defined in the dictionary as... "tani"). I first encountered it in Chinese poetry, and that's still what it invokes for me: the sort of sweeping yet intricate nature-talk that the Japanese tanka form is physically incapable of reproducing. So, in an otherwise simple tanka like this, 溪 is evocative and charming, linking Saigyō to the grand continental tradition of mountain hermitry.

But is this interpretation "authentic"? Maybe Saigyō really wanted to emphasize the river in his valley (this seems unlikely, though, as it's not relevant to any other part of the poem). Or maybe he didn't even use this character here — maybe it only appears in the edition I have due to some weird decision by editor Sasaki or some intermediate scribe. (This poem is actually marked with the ○ that indicates that Sasaki interpolated it into his edition from a book other than his main source, so maybe it's a quirk of this non-main text he was referencing.)

The next big point of interest in the poem is that Saigyō finds joy in the uguisu staying in its nest, as opposed to every other tanka poet ever, who waxed joyful when the uguisu left its winter nest. As poem 14 in the Kokin waka shū sez:

うぐひすの谷よりいづるこゑなくば春くることをたれかしらまし
Without the voice of the uguisu come out of the valley, who would know when spring came? (Ōe no Chisato)

Unlike Ōe no Chisato, though, Saigyō lives in the valley. It makes sense that he would appreciate the uguisu still nesting there with him. And, in fact, the Sanka shū contains many poems about uguisu and their nests, which make it even clearer what Saigyō means. Here's a string of four with the heading "On the disappearance of the voice of the uguisu from the valley where one lives" (住みける谷に鶯の聲せずなりにければ):

ふる巣うとく谷の鶯なりはてば我やかはりてなかむとすらむ
鶯は谷のふるすをいでぬともわがゆくへをばわすれざらなむ
鶯はわれをすもりにたのみてや谷のほかへはいでてゆくらむ
春のほどはわが住む庵の友になりてふる巣ないでそたにの鶯

"The uguisu are long gone from their nests; maybe I should cry in their place."
"Though the uguisu have left their old nests, I hope they don't forget where I am."
"Will the uguisu ask me to watch their nests when they go out from the valley?"
"Don't leave your nests this spring, o uguisu of the valley; stay by my hut and be my friend."

That last one is particularly relevant, I think.

Are we missing anything else? Almost certainly, but let's review. Because the nightingale tends to spend its time in mountains and valleys, it is symbolic to an extent of hermitude as well as spring. Their call is sometimes transcribed "Hō-hōke kyō," which might seem relevant to a poem written by a monk — but no! Yamaguchi Nakami 山口仲美's Chin chin chidori informs us that this onomatopoeia wasn't thought up, or at least wasn't widespread, until the Edo period. When Saigyō was writing, it seems that people mostly thought it said "Hitoku, hitoku" ("Someone's coming, someone's coming"), or "Tsūki-hi-hoshi" ("Mooon, sun, stars").

Besides, in another poem Saigyō more or less explicitly rejects any uguisu-religion connection:

鶯の聲にさとりをうべきかは聞くうれしさもはかなかりけり
Find enlightenment in the uguisu's call? [No,] the joy of hearing that is fleeting too

What else? Well, maybe there's some irony in Saigyō rejoicing in the uguisu's lingering when one of his most famous poems is a lament about failing to leave the capital and worldly things behind despite having renounced the world (世の中をすてゝ捨てえぬ心地して都はなれぬわが身なりけり)... Or maybe we're supposed to read it as meaning "the voice of the uguisu that [seems to] linger in the nest [after the actual uguisu has left]"... but there comes a point at which you have to either re-enrol in grad school or move on to the next 31 morae.