The composer Jeff Harrington recently pointed to a page transcribing the contents of H.P. Lovecraft's Commonplace Book, here. Lovecraft left enough interesting ideas as unused material for several careers worth of weird fiction, heck even a few weird operas. (I have to admit to never having read Lovecraft; maybe I should remedy this.)
To some extent, blogs are performing, in public, the function of the Commonplace Book, the place to keep record of one's own education, jotting down gathered notes and quotes, observations, ideas. This page actually began as a more-or-less smooth transitition from the marginalia I habitually scribbled on the edges of sketches and scores. But being public has altered the scope of this project. It tends to be more political and, though something of a record of my current musical obsessions, it's not as iniitmately connected to my compositional projects as my marginalia was, indeed, I find myself rather shy about writing directly about my own compositional concerns. At the same time, my entire cogitating-sketching-composing-editing procedure has changed quite a bit. Whereas I used to be fairly rigorous in the march from sketch to score, leaving a substantial paper trail, I now do more work directly in notation software now and try to keep my sketches to bits of paper (usually A6 size) that I scatter around my desk while working — some bits of notation, formal schemes, reminders of work to be done etc. — and then brush them aside into the waste basket when no longer needed. (I think having a crowded house with kids and dog underfoot has made me much less patient about maintaining an archive of sketches (on the other hand, in my role as publisher, I'm fairly obsessive in maintain any bit of paper from the other composers in my catalog.) On the other hand, I have several hundred uncatalogued pieces in various stages of development in the form of computer files for notation programs; I have no idea how or if I'll maintain these. )
But the idea of keeping an idea book like Lovecraft's, for my music, especially for all the plans and fantasies for work-to-come, is very attractive. I do have a short list with titles and short descriptors of pieces I'd like to write (titles are very important to me), but it's just another piece of paper hanging on the wall before my desk, not a real book. An idea book is something like a diary, but more like a dream diary than a record of daily and mundane accomplishments. Like diaries, however, I think that the very "bookishness" of such a document gives it a degree of seriousness and commitment that is useful for a composer. La Monte Young, for example, has long kept an Idea Book (and some of his ideas, from the peek I've had, are really quite wonderful and surprising, in particular a pair of operas.) Do you keep an idea book?