Lying on your back in late summer, watching birds cross the sky, is about as low-stakes as a moment can get, which is exactly why Edward Thomas chooses it. His speaker looks up, sees a swift, and only later understands that this was the last he would see until spring. The poem's central idea is quietly unsettling: we almost never recognise a "last time" while it is happening. The meaning of a moment arrives only after the moment has gone.
The first stanza turns that thought into one long, slightly tangled question. "How at once should I know" asks how anyone could know in the instant itself. The scene is deliberately relaxed. "Stretched in the harvest blue" gives us a body at ease under a sky coloured by the season, and the word "stretched" suggests someone not paying the kind of attention a farewell would demand. Then comes the image that holds the poem together: "the swift's black bow." The swift's narrow, curved wings really do resemble a drawn bow, and that sharp black against soft blue is the only hard edge in the picture. A bow can also be something made on leaving, though the poem only hints at that. The stanza's last word, "due," belongs to timetables and bills. The swift's return is something owed, as regular as a calendar.
The form is neat but never stiff. Both stanzas have seven lines and rhyme ABABCCB. In the first, "blue," "view" and "due" are full rhymes, tying together the sky, the sight and the promised return. Lines five and six shrink to three syllables each, "Another day / Until next May," so that the long stretch of months is squeezed into two quick steps. The last line then lengthens again and ends on a question mark, and Thomas offers no answer. Most of the words are single syllables, and the slightly inverted "Again it is due" sounds like someone thinking aloud rather than performing.
In the second stanza the rhymes loosen. "Alone," "done" and "gone" are near-misses rather than true matches, and that small mismatch suits a poem about things slipping away. The lines "The same year after year— / But with the swift alone" are compressed enough to be read in more than one way, but the contrast is clear. The swift's disappearance comes round every year, and so does its return. "With other things I but fear" (here "but" means "only") that they will end with no such promise. The swift becomes a small, repeatable rehearsal for losses that have no "next May." Then "Suddenly" gets a line to itself, a single word that arrives as abruptly as the thing it names. The stanza closes on its cleverest turn: "And I only see / Them to know them gone." The line break leaves "I only see" hanging, and what follows folds seeing and knowing into one. What he finally sees is an absence.
What makes the poem significant is how much it gets out of how little. There is no mention of death or grief, only a bird, a sky and a man on his back, yet the feeling of something unnoticed and gone lingers. Readers who know that Thomas was killed in the First World War may hear a darker undertone in "over and done," but nothing in the text says so, and the poem's power is that it doesn't need to. It sends us back to ordinary afternoons with a slightly sharper sense that this one, too, might be a last.