On April 23rd, George Szirtes and some open-mikers gave a standing-room-only Cambridge CB1 audience an entertaining evening of sonnets. The sheer volume of Szirtes' output can be intimidating. His 2008 "New & Collected Poems" is 520 pages long, and he's kicked on since then, extending his range. Focusing on the sonnet only restricts him somewhat - he said he's written over 300 of them!
He highlighted the longevity and flexibility of the form. Those two features are probably related, but there might be psychological (or even physiological) reasons why the sonnet endures. Don Paterson in his "101 Sonnets" was prepared to include "any poem with fourteen lines". "The Reality Street Book of Sonnets" cast its net wider (download the Introduction). Szirtes didn't want to be pinned down to a definition, instead suggesting that a sonnet is like a room, with certain expectations of scale, proportion, purpose and intimacy that the poet can choose to ignore.
He studied Fine Art in London and Leeds, and was asked in the Q&A if there was a strong visual element during composition. After all, many of the sonnets he read were about colours. He replied that there was always a dialogue with words, each line/word capable of changing the course of the poem. Rhyming in particular can take you where you didn't plan to go. You need to be ready to follow. Curiosity and a non-doctrinaire openness to impressions seem to be a source of word production for him - liking a youtube clip, a colour, or a goal may provoke him to wonder what there is in the phenomenon that's interesting him.
I sometimes look upon the sonnet as a franchise. You buy into it to take advantage of the image. You might add some local variation (curried burgers maybe) but go too far and the parent company might disown you - you have a duty to the brand as well as your customers. I have trouble writing sonnets. Finding them a technical challenge I become too much of a slave to the brand. According to my notes I've published 9 sonnets. I don't recall most of them. Two are acrostics, of which I'm unjustly proud (one, called "Going down", reads "Cambridge Blues" down the left margin). I've recently entered a sonnet for the Ware Poetry Competition but only because the content determined the form. So like a fool I followed.