The poem was first published in his collection Mountain Interval in 1916. This poem comes to mind more often than you might think for me, sometimes it's "But that he knows in singing not to sing", although more often, it's the closing two lines, "The question that he frames in all but words/Is what to make of a diminished thing."
The Oven Bird
by Robert Frost
There is a singer everyone has heard,
Loud, a mid-summer and a mid-wood bird,
Who makes the solid tree trunks sound again.
He says that leaves are old and that for flowers
Mid-summer is to spring as one to ten.
He says the early petal-fall is past
When pear and cherry bloom went down in showers
On sunny days a moment overcast;
And comes that other fall we name the fall.
He says the highway dust is over all.
The bird would cease and be as other birds
But that he knows in singing not to sing.
The question that he frames in all but words
Is what to make of a diminished thing.
Form: It's got ten syllables to each line (Frost treated "showers" and "flowers" as single-syllable words here), and it ends decidedly iambic, although it starts a bit shifty, if you must know. It has its own peculiar rhyme scheme (AABCBDCDEEA'FA'F), which makes it a "nonce" form -- a nonce form is a poetic scheme invented for a particular poem. This one has fourteen lines, so it's kind of like a sonnet, but it doesn't fall into a recognized rhyme scheme, not even as a Pushkin, or Eugene Onegin, stanza. Still, I think it likely started as a sonnet, and that Frost decided deliberately to depart from the usual sonnet rules to create something new -- a lovely bit of form meeting function, I believe, if you believe, as I and some others do, that Frost was announcing a new kind of poetry for a changing world.
Further, although I haven't yet gotten my hands on a copy, the book On the Sonnets of Robert Frost: A Critical Examination of the 37 Poems by H.A. Maxson includes "The Oven Bird" as one of Frost's sonnets, and apparently supports this conclusion by including references to Frost's own prose writings where he discusses his own poem as a sonnet. Also, as has been noted in multiple sources, Frost was pretty forthright about his playing around within the sonnet form. "The sonnet is the strictest form I have behaved in, and that mainly by pretending it wasn't a sonnet, " Frost once wrote to Louis Untermeyer. I'd argue that he pretended it wasn't a sonnet by using shifty rhyme schemes (and, occasionally, shifty metre as well).
Dicussion and analysis: If you'd like, you can read this as a simple nature poem -- an observation on the call of the oven bird (a loud "Teacher, Teacher", if you didn't know). The oven bird is loud at a time of year when many other birds are not, and Frost tries to decipher what his call means. And if that's how you read the poem, it is an excellent poem.
The poem also works on a deeper level. The oven bird becomes not just the "teacher" implicated in his call, but is a symbol representing the poet. This poem was, in some respects, a war poem.* It was written in 1916, and reflects the sense that it is the world that has diminished, with "dust . . . over all". And the poet is left to ask what is to be done. Can art go on? Can poetry continue in the face of such ruination? (This is not unlike the question implied in Edgar Allen Poe's poem, "Sonnet: To Science", in which Poe explores the effect of science on creativity and myth.) In the early twentieth centuries, with the horrors it brought along with it in the form of trench warfare, mustard gas, and mechanized warfare, and in its greed and vanity (think about the robber barons we studied once upon a time, and the practice of child labor, and the inhuman working conditions faced by so many people), how can one respond to such indignities and horrors?
Another reading of the poem focuses closely on the line "he knows in singing not to sing." Some commentators believe this line is the answer to a question posed in an earlier poem by a Victorian poet named Mildred Howells, "And No Birds Sing", a Keatsian poem in which Miss Howell asks how the bird can sing with winter approaching.
There comes a season when the bird is still
Save for a broken note, so sad and strange,
Its plaintive cadence makes the woodlands thrill
With sense of coming change.
Stirred into ecstasy by spring's new birth,
In throbbing rhapsodies of hope and love,
He shared his transports with the listening earth
And stormed the heavens above.
But now how should he sing—forlorn, alone—
Of hopes that withered with the waning year,
An empty nest with mate and fledgelings flown,
And winter drawing near?
Frost's line, "he knows in singing not to sing," is seen as meaning that silence itself is part of the song. And/or that the oven bird, here representing the poet, is rejecting the old school of thinking and finding a new way to express himself. And this particular bird finds a way to express himself -- loudly, as it turns out.
Finally, others have seen Frost's poem as a criticism of encroaching development -- an environmental poem with a Thoreau-like sensibility, based on the line "the highway dust is over all."
*Perhaps my favorite of the war poems, and one of the best-known, is Wilfred Owen's "Dulce et Decorum Est", which I believe will be a topic for another day. The title comes from a line in the poem Dulce et decorum est pro patria mori (It is sweet and seemly to die for one's country).