"No Second Troy" looks just like a sonnet. Surely it must be a sonnet, right? But then you count the lines and notice that there are only twelve, whereas a true sonnet has fourteen. Sigh.
You can still call it a modified sonnet if you want, or you can call it a "douzaine," which is French for "a dozen." Or you could call it a "dozen," but don't blame us if the French get angry.
The most famous example of a "douzaine" in English is Shakespeare's Sonnet 126, his farewell poem to a young nobleman known by critics as the "fair youth." We're sure Yeats would have known of the poem. Sonnet 126 is about how nature will eventually cut the man's life short, so it makes sense that the poem is cut short.
It's less clear why Yeats chose to have twelve lines in this poem instead of fourteen, except that he probably felt he didn't need those extra lines to make his point. You could get all symbolic and say that the spirit of Maud Gonne "burned" the last two lines like she would have burned the second Troy. But now we think you're just going too far, you crazy Shmooper.
As in a Shakespearean sonnet, the rhyme scheme divides the poem into three quatrains, or groups of four lines (the lack of a final rhyming couplet accounts for those two missing lines). Grammatically, though, the poem is divided into two sets of five lines and a couplet. The rhyme scheme is: ABAB CDCD EFEF. All of the rhymes are regular except for the slant rhyme of "this" and "is" (lines 9, 11).
Also like a Shakespearean sonnet, the meter is iambic pentameter, although less regular than the Bard would have used. What the heck does that mean? Well, "iambic" refers to the pattern of stresses in the line. An "iamb" is an unstressed syllable, followed by a stressed syllable: da-DUM. "Pentameter" means that there are five ("penta," like a pentagon) iambs in the line: da-DUM da-DUM da-DUM da-DUM da-DUM. Easy, right? Let's look at those iambs in action…
Or hurled | the lit|-tle streets | u-pon | the great.
The loose iambic pentameter gives the poem a conversational sound.