@The Pentacle Queen,
PQ: I only found this thread just now. Right up my alley, as you know. Various life circumstances have kept me away from A2K for quite a while.
Since Taruskin was partly the impetus for your question, you can read what he has to say about it in the preface to his Oxford History
. As best as I can sum it up: a historian tells history as it happens as objectively as possible while a critic cites historical episodes as illustrations of, or in furtherance of, some broader trend or ideology. The example Taruskin uses is the Shostakovich controversy: in the Oxford History
, he reports the facts of Shosty's memoirs and their aftermath, while elsewhere he reports his opinion on the matter. A reader unfamiliar with Taruskin's stance on the Shosty wars is not meant to be able to learn what it is by reading the Shosty chapter of the Oxford History
That said, there are of course many instances where history and criticism are not easy to keep separate, and some scholars are better at it than others.