Should Bach be played on Bach's instruments?

Maybe, and the people who study it disagree. Historically informed performance, or HIP, aims to be faithful to the approach, manner and style of the era in which a work was conceived. That usually means period instruments or reproductions: an ensemble playing Bach may use reproduction Baroque violins instead of modern ones, to try to recreate the sound of a Baroque orchestra.

The difficulty is evidence. No recordings exist from before the late 19th century, so HIP is largely derived from musicological analysis of texts. The reference pitch of earlier music cannot generally be read as the pitch used today; one researcher found violinists having to retune by a minor third to play at neighbouring churches. Composers assumed the player would choose the temperament, and never wrote it in the score. At the height of the revival there was even a debate about vibrato, with many advocates trying to eliminate it in favour of the "pure" sound of straight-tone singing.

Then come the critics. Richard Taruskin, one of the most sceptical voices, holds that HIP is itself a 20th-century practice influenced by modernism, that we can never know exactly how earlier music sounded, and that supposedly authentic performances embodied a wish list of modern values. Roger Scruton charged that it has frequently cocooned the past in phoney scholarship. Defenders reply, in John Eliot Gardiner's words, that their enthusiasm is not for an unattainable authenticity but for a refreshing alternative to the monochrome symphony orchestra. Meanwhile the label "historically informed" is now preferred to "authentic", because it acknowledges the limits of what scholars know.