What does this mean: Critics ought to be guardians of quality, not purveyors of opinion.

In the Strad magazine, and on his blog, Slipped Disc, English music critic Norman Lebrecht is posing the age-old question of what a critic's role should be.

It's a debate I have with myself, my manager(s) at the Star, with readers and music lovers every day.

I was particularly intrigued by the first comment on Lebrecht's blog, from someone named Andrew. He wrote: "One directer I know said that critics ought to be guardians of quality, not purveyors of opinion."

This is one of those elegant little epigrams that sounds excellent, but doesn't hold up that well. It sounds good because it sets up a mutable, subjective thing, against something eternal and objective.

But is that what quality is? And quality of what?

I think the best illustration of this little minefield comes from music competitions. The start of the Tchaikovsky competition is a great excuse to note that the laureates of the hundreds of competitions that are held every year have been singled out for the quality of their performances, but that does not assure them of engaging audiences or building a career.

There is another trait -- or combination of traits -- that helps make a successful musician. And others yet that make for a satisfying evening of music. And still others that make for a great recording.

Now try to describe this experience using simple, declarative sentences, in 400 words or less.