An important way to identify sound patterns in a poem is to listen to the poem read aloud, for this is the way the author intended the work to be experienced. A great deal of what we perceive about the musical quality of the poem and the exquisite imagery poets often include in their work is to listen to the poem as opposed to reading it silently.
The rhyme scheme—which often gives a poem a musical feeling—is not as obvious in Frost's "The Road Not Taken." I believe this is the case because the poem consists of five-line stanzas (or sections) rather than those with four lines (which are more traditional). Where many popular poems of the past were consciously infused with a lilting movement (sway) using rhyme and meter (rhythm), Frost uses rhyme to draw attention to images that are presented—using sound—but not giving his work the steady ebb and flow often so popular in other poems. (See pattern of rhythm and rhyme in The Rime of the Ancient Mariner by Samuel Coleridge.) This may be because the topic at hand does not speak of love or nature's beauty, but about making choices in life that cannot be undone—a very serious topic.
In the first stanza, wood, stood and could all rhyme, but we don't read the poem in a way that the words stand out with a pattern of sound. The poem is read without pause at the end of the line unless there is punctuation to denote such a pause. This pause allows us to more easily follow the important statements Frost is presenting through this piece.
Two roads diverged in a yellow wood,
And sorry I could not travel both
And be one traveler, long I stood
And looked down one as far as I could
To where it bent in the undergrowth; (1-5)
For example, we should pause in reading at the end of line one and in the middle of line three, as that is what the use of a comma requires. "Long I stood" at the end of line three draws our attention and makes us want to pause slightly because of the words themselves, and the author draws our attention back to "wood" at the end of line one.
I hear the pattern of sound in:
Two roads diverged in a wood, / And sorry I could not travel both and be one traveler, / Long I stood...
The next stanza has plenty of places for pauses, based on punctuation: for me the pattern of sound created is like the mind's dance back and forth in trying to make a decision:
Then took the other, as just as fair,
And having perhaps the better claim,
Because it was grassy and wanted wear;
Though as for that the passing there
Had worn them really about the same, (6-10)
What I hear are two ideas that seem to contradict each other as two sides of an argument in one's head might sound, in trying to rationalize why he made the choice he did. The reasoning for one path takes place amid commas, and ends with the semi-colon; at this point attention is turned to the second path.
In the next stanza, there is continuing pattern of sound:
And both that morning equally lay
In leaves no step had trodden black.
Oh, I kept the first for another day!
Yet knowing how way leads on to way,
I doubted if I should ever come back. (11-15)
Following the pauses created by punctuation, this stanza starts with a statement of fact—emotionless...that both paths on that day seem undisturbed. However, on the third line, a comma and an exclamation point are used. The exclamation of "Oh" draws the reader's ear, announcing that something important is to follow. It is the announcement by the speaker that he decided unequivocally to make a sudden and final decision to pass the first path. The use of the word "Yet" also gives the reader (or listener) pause. By its nature, it is used like the word "but." The speaker realizes after the decision is made that the idea of returning another day is not likely in that life carries us to unexpected places. The reader then arrives at the last section.
I shall be telling this with a sigh
Somewhere ages and ages hence:
Two roads diverged in a wood, and I—
I took the one less traveled by,
And that has made all the difference. (16-20)
In the final stanza, there is an element of coming to terms with a truth. The word "sigh" and the phrases "ages and ages" change the previously charged mood to one that is staid and unchanging. "Sigh" slows the movement of the poem's action. The energy and conviction found in line thirteen has been replaced by a sense of moving backward rather than forward. The ear catches the repetition of "ages and ages," letting us know that the speaker is aware of the long-reaching effects of his almost casual choice to take the second path. The repetition acts to the ear like an echo. The speaker solemnly looks at where he stands on that path, remembers the unknown possibilities the two paths offered, acknowledges his choice to follow a path not taken by the masses, and experiences the realization—ringing with finality—that the choice altered everything that was to follow.
While sound in a poem with generally refer to a rhyme scheme and to the poem's meter, what reaches me first in terms of a pattern of sound is the way Frost uses punctuation to support the structure of the important ideas he is sharing—letting us pick up on first the excitement, then on the sense of the cavalier manner of youth, and lastly, the implications the most casual decisions may have upon our lives.
From a more traditional position, there is a rhyme scheme or pattern of rhyme found in the last word of each line. If we assign a letter to identical sounds and a new letter to a new sound (using A and B), the pattern is:
A B A A B
For instance, in the first paragraph wood, stood and could rhyme (A) in lines 1, 3 and 4. A new sound (B) is introduced in lines 2 and 5: both and undergrowth.
With this choppy and lopsided pattern of rhyme (sound), the author may be presenting the symbolic image of a path that moves from side to side, impossible to predict, potentially offering the unexpected as the path shifts—and even surprises when it takes a turn. The shifting could be supported with the ideas found in the first three stanzas, while the turn occurs in the last stanza—for this is when the mood of the poem changes dramatically.