Mostly Petrarchan Sonnet
"Design" is a very impressive sonnet. A sonnet is a poem composed of fourteen lines that usually develops some sort of argument and has a shift or turn in it (the technical term for this turn is the volta). There are three different types of sonnets: Spenserian, Petrarchan, and Shakespearean. Of these, Petrarchan and Shakespearean are the better-known, and "Design" actually combines elements both.
We can say that it's mostly Petrarchan, because its first eight lines follow an ABBAABBA rhyme scheme and they form a very complete first unit, which we call an octave. But then things get weird. The last six lines have a unique rhyme scheme: ACAACC. By rhyming the last two lines, he gives us a classic Shakespearean couplet, also known as a heroic couplet. Shakespeare was famous for wrapping up his sonnets with these last two rhyming lines that sounded a lot like punch lines. We don't get a punch line in this poem, but the last two lines do answer the questions brought up earlier in the poem. So it certainly flirts with being a Shakespearean sonnet at the end.
The main thing to see and be amazed by here is how few rhyme-sounds there are. English is a tough language for rhyming poetry. We aren't like those Europeans with their easy-rhyming romance languages. So we usually don't write poems that restrict our rhymes. But Frost says bring it on. The whole poem only uses three different sound endings and seven lines (half of the whole poem) ends with an "ight" sound. For any of you who have tried to write in rhyme, you know that this kind of restriction is officially… crazy. Frost is really showing off in order to make a point—the intricate design we see points us toward a Designer (in this case, ol' Frosty-pants himself).
The meter of the poem is just what we would expect from a sonnet: iambic pentameter. Iambic pentameter might sound weird at first, but if you read enough English poetry, you'll learn to get used to it. (We got so used to it that we named our dog Iambic Pentameter.) All this means is that each line in the poem is composed of five iambs. Each iamb is a unit composed of one unstressed syllable followed by a stressed syllable. It ends up sounding like: daDUM, daDUM, daDUM, daDUM, daDUM. Look at line 1 for example:
I found a dimpled spider, fat and white.
Most of the time, poets vary their meter pretty regularly. In fact, it's pretty uncommon to see more than a few lines of "perfect" iambic pentameter in a poem, especially one written in the twentieth century. Modern poets got a lot less picky with their form and meter, mainly choosing to go with free verse. But Frost was a stickler. This sonnet has eight lines of perfect iambic pentameter (lines 1, 4, 5, 8, 10, 11, 12, 13). Three others (lines 6, 7 and 9) simply have an extra unstressed syllable thrown in (which in the poetry world doesn't really count off too much for). That leaves us with only three real variations—impressive stuff.
The variations all use the same trick. Look at lines 2, 3 and 14. Rather than begin with "daDUM, daDUM," they start with two unstressed and then hit us with the stressed: "da da, DUM DUM." For crazy form and meter bonus points, you might want to know that, technically speaking, this is a pyrrhic followed by a spondee. The effect of the first two, especially at the beginning of the line and toward the beginning of the poem, is to add momentum. We move quickly over those unstressed syllables and then we hammer on the stressed ones. This is a good move for Frost as the first three lines are setting up a narrative. The last line begins with two soft syllables so it creeps up on the reader. We ended line 13 with that dash, which held us in suspense. It's like the poem ended there and then he slowly, quietly begins speaking again.
If you haven't caught on by now, a good word to describe this poem's form would be "designed." Clearly, Frost is the master of everything that happens in this poem, right down to the syllable. Even if the content may be asking questions about who's running the show of life generally, we're left with no doubts that we're in the presence of a great Designer of the poem itself.