Edward Thomas starts by confessing a daydream, then spends the rest of the poem walking away from it. Beside a bright, fast brook, the speaker finds its beauty tempting him to imagine "a time / Long past and irrecoverable" when such a stream would have had its own goddess, "a nymph whose soul unstained / Could love all day, and never hate or tire." Then he drops the fantasy, calls it a "poison," and gives his attention to what is actually there: water, flowers and small brown birds. The central idea is that the real, unimproved world is enough, and that the sedge-warblers' wordless song holds a kind of wisdom no education supplies.
The form acts out this swerve. The first ten lines are one long, winding sentence. The subject, "any brook," has to wait until line six for its verb, "would bear," and the dream keeps unspooling after that. The vocabulary is deliberately "poetic" and old-fashioned: "clime," "divine," "nymph," "kin." It sounds like a poem that has read too many other poems. The loosely iambic five-beat lines and neat early rhymes (time/clime, brass/grass) make it smooth and lulling. But the stanza never quite closes. Its last sounds, "unstained" and "tire," are answered only across the break by "drained" and "desire." The dream is undone by its own rhymes, and the poison is drained between one stanza and the next.
The second stanza swaps myth for particulars: "water-crowfoot," "chestnuts," "willow twigs." Even so, the goddess is not simply thrown out. The brook is "Clearer than any goddess or man's daughter," and it does what a nymph might, since it "combed the dark green hair" of the weeds streaming in the current. The real water takes over the dream's work without needing a figure to embody it. Thomas's word for the drifting petals is homely and almost unappetising, as they "curdled to one sheet." It is exactly right for a scum of white blossom, and nothing like the language of the first stanza.
The birds get the same treatment. They cling "so light" to the willow twigs, and they "sang longer than the lark," the traditional poets' songbird, outlasted here by a plainer rival. The sounds of the lines follow what they describe. "Quick, shrill, or grating" is clipped and rough, while "Gushing through narrows, swirling in the pool" runs liquid. The song somehow suits both "the heat / Of the strong sun" and "the water's cool," holding opposites together without strain.
The ending is where the poem is most quietly clever. The song "lacks all words, all melody, / All sweetness almost," and the hedge "almost" is honest. Then comes the line "Than sweetest voice that sings in tune sweet words," in which "sweet" appears three times, as if the poem were using up the word before setting it aside. The birds are "wisely reiterating endlessly," so their wisdom lies in persistence, not argument. The final line, "What no man learnt yet, in or out of school," ends with a gently teasing shrug at formal learning. Its last word also rhymes with "cool" and "pool," bringing the poem back to the water, while "endlessly" echoes "melody" and "me."
The poem matters because it is honest about temptation. Thomas does not sneer at the dream. He admits it nearly intoxicated him, and he uses its own fancy language to show how easily the imagination can crowd out the thing in front of it. What replaces it is a way of looking: patient, exact, and willing to find beauty in something shrill and brown and repetitive. There is a paradox here too. A poem, which is made of words, ends by honouring a song that has none, and by admitting that the best of May cannot be taught.