How do you decide what form to use in a poem?

I tend to think that poems come pre-packaged, and that when the idea suggests itself to me the form comes with it: I sort of see it in my mind's eye - particularly with poems that come as blocks of text, you know, that look like gravestones or something like that, or those that come as quatrains and look like hymns. They don't always stay in that form because when I start writing I'll sometimes notice that there is a pattern of language, perhaps a rhyme or a repetition, and that might suggest some further, you know, physical form or shape on the page, but I think I do imagine these things to be predetermined in some way - that they are somehow in concert with the whole idea of the poem and with the style of the poem because I don't think I would ever embark on a poem unless I knew its style - style is everything to me, in writing. You know, the subject is almost - well it's not kind of insignificant but the style is the main thing: I think that is what people are interested in in poems.

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