Half the trees are dead, and the living half cast hardly more shade than the corpses. It is an unpromising place for happiness, yet it is where Edward Thomas locates a gladness that arrives "without cause." The poem recalls a short walk down a ruined avenue of ash trees. If they once led to a house, they saw it fall long ago. It then follows what that walk has become: a feeling any ash grove, "far from those hills," can bring back. Its central idea is that some moments of peace are given rather than earned, and that they outlast the place where they happened.
The grove is a threshold, and the poem's key word for it is "Interval," capitalised as if it were a place in its own right. It lasts "scarce a hundred paces," but those paces are "sweeter than sweetest miles," so Thomas measures the stretch and then says measurement doesn't apply. Inside it, "nothing at all" can get in, not even "the spirits of memory and fear with restless wing." Memory and fear become winged creatures that cannot "climb down in to molest me over the wall." The speaker passes through the walls at both ends "without noticing," so the peace seems to have no edges. The poem's repeated "without" is worth noticing too: "without cause," "without noticing," and finally "without search or desert or cost." Gladness comes with no reason, no effort and no merit, and the last line shows how completely it is a gift.
The form is more carefully built than the relaxed, walking pace suggests. The lines are long and loose, roughly five or six beats each, with a speaking rhythm that sometimes rolls and sometimes stumbles, so the printed page has to fold them over. Underneath is a chained rhyme scheme. In each four-line stanza three lines rhyme and the third, an odd one out, supplies the rhyme for the next stanza. "Fall" in the first stanza becomes "Interval," "all" and "wall" in the second. "Wing" leads to "noticing," "bring" and "sing," and "ghost" leads to "uncrossed," "lost" and "cost." Each stanza hands something on to the next, and sentences also spill across the breaks ("over the wall // That I passed through"). The effect is of a walk that doesn't stop at boundaries, matching the unnoticed walls. The final stanza has no successor to pick up its odd word, so "die" is left without a partner. The line that contains the something "unwilling to die" is the one that refuses to be tied off.
The poem's imagery keeps the living and dead side by side. Half the grove is dead, and the speaker returns as "a ghost" with "a ghostly gladness." He is as much between states as the trees are. The song is the most delicate image: he feels the gladness "as if I heard a girl sing / The song of the Ash Grove soft as love uncrossed." The song gives the poem its title and also names the tree, so grove and music are one. The word "as if" matters, because nothing is actually heard. The song is lost "in a crowd or in distance," yet in that moment something is "unveiled," as though a curtain were drawn back on a feeling that was always there.
There is also a quiet paradox. The Interval was a place where memory could not enter, yet the poem exists only because the speaker now remembers it. Memory, which he said was shut out, is the very thing that lets him walk the grove again. The poem doesn't resolve this. It lets the present tranquillity be "the same" and also a ghost's, borrowed and a little unreal. That honesty gives it its weight. Thomas claims neither that the past can be recovered nor that it is gone. He says a moment can return in faint form, wherever there happen to be ash trees.
The poem is significant for its restraint. It makes no large announcement about time, loss or happiness. It gives a hundred paces, a wall, a half-remembered song and a final sentence that sounds almost astonished at its luck. For a student reading closely, the pleasure is in seeing how much the small details carry: the repeated "without," the rhyme that passes from stanza to stanza, and the one word, "die," left hanging at the end.