The sonnet is like the legendary camel which, having put its nose into the tent to keep it warm, soon makes himself at home. Originally an Italian import, it has become the most popular, almost the standard form in English, with thousands of published examples produced by practically every major and minor poet since before Shakespeare.
Everyone should write at least one sonnet in a lifetime.
Sonnets are fourteen-line poems, period. They exist in every line length, with every rhyme scheme imaginable, or with no rhyme scheme at all. The more or less standard sonnets, however, fall into two types: Italian and Shakepearean.
Of these, let's work with the more popular, more elaborate, and at least formally more difficult form. The Italian sonnet was popularized by the Italian poet Petrarch in the fourteenth century, when he wrote a whole bunch of them about his hopeless love for Laura (she seems to have been married). Hopeless lovers have imitated him ever since.
Italian, or Petrarchan, sonnets are usually written with a long line of five beats (da-DUM, da-DUM, da-DUM, da-DUM, da-DUM). They break down into one eight-line stanza, that tells an experience or expresses a thought or feeling, and a six-line stanza, that contrasts with, resolves, or comments on the first part.
The eight-line stanza, called an octave, uses two rhyme words. The first line rhymes with the fourth, fifth, and eighth lines; the second with the third, sixth, and seventh. Confused? Here is the octave of a sonnet by the best sonneteer of the twentieth century, Edna St. Vincent Millay:
What lips my lips have kissed, and where, and why,
I have forgotten, and what arms have lain
Under my head till morning; but the rain
Is full of ghosts tonight, that tap and sigh
Upon the glass and listen for reply,
And in my heart there stirs a quiet pain
For unremembered lads that not again
Will turn to me at midnight with a cry.
See? "Why" rhymes with "sigh," "reply," and "cry"; "lain" rhymes with "rain," "pain," and "gain."
So now she has expressed her feeling (Loneliness? Regret?) In the six-line finale (the sestet), she is going to make the feeling more vivid still by resorting to a comparison of her situation with that of a tree in winter which, cold and abandoned, seems to have only a faint, nonspecific sense of loss:
Thus in the winter stands the lonely tree,
Nor knows what birds have vanished one by one,
Yet knows its boughs more silent than before:
I cannot say what loves have come and gone,
I only know that summer sang in me
A little while, that in me sings no more.
Note the rhyming here is "tree" (line 1) rhyming with "me" (line 5); "one" (line 2) rhyming (imperfectly) with "gone" (line 4); and "before" (line 3) rhyming with "more" (line 6). We could represent that using the scheme abcbac. Actually, that's trickier than most sestets. The usual is either abcabc, ababab or, if the poet wants a summarizing last two lines, ababcc.
Does that seems too hard? I estimate that probably a million sonnets are written nowadays worldwide, by poets young and old, of all possible levels of skill. Why not you?
A bigger question is, why bother? Well, you can't know how satisfying, how pleasant, and even how liberating the sonnet can be until you try one. Millay, in a sonnet about writing a sonnet, puts it best, as usual:
I will put Chaos into fourteen lines
And keep him there; and let him thence escape
If he be lucky; let him twist, and ape
Flood, fire, and demon--his adroit designs
Will strain to nothing in the strict confines
Of this sweet Order, where, in pious rape,
I hold his essence and amorphous shape,
Till he with Order mingles and combines.
Past are the hours, the years, or our duress,
His arrogance, our awful servitude:
I have him. He is nothing more than less
Than something simple not yet understood;
I shall not even force him to confess;
Or answer. I will only make him good.
Conrad Geller's Series on Poetic Forms: