The world's largest performing arts festival is back in Scotland's capital for three weeks of theatrical chaos, featuring over 4,000 shows. As always, the Fringe brings with it the annual existential crisis: what does a star rating actually mean, and why do we let it define our artistic worth?

Our comedy critic, Brian Logan, is fielding reader questions live, and the queries are already diving into the murky waters of review culture. One reader, Achhca, asks: "Reviews at the Fringe seem to have extra weight to them, especially the exact star rating - four stars can go on the poster, three stars may as well be zero. What are your criteria for stars, and is it informed by the knowledge that a 4+ will end up stapled on posters across the city?" A second reader, brion, chimes in: "Why have you offered so few five star reviews? What is your rubric for a five star score?"

Brian's response is a masterclass in reluctant star-giving. "I try to think about star ratings as little as possible," he admits. "My job, as I see it, is to write something insightful, respectful and hopefully entertaining about a show; and to express all I have to say about that show in words. At a stretch, I recognise the usefulness, to some, of then appending a star rating to that review. But I wish we didn't have to. It's reductive and dumb." He laments that his own children ask 'what did you give it?' instead of 'what did you think of it?' - a parenting fail that probably haunts him more than any bad review.

But Brian isn't above a little levity: "Let's not take ourselves too seriously! There was once, reputedly, a critic who never gave three-star reviews because he knew no one would read them. But most shows are three-star shows - i.e. good, enjoyable, competent if unexceptional. I'll try to err on the side of enthusiasm whenever I can. God knows my own work has received enough two- (and lower) star reviews over the years. I know how depressing that is."

On whether reviews actually matter, Brian is surprisingly philosophical: "Matter to whom? They matter to me. My experience of art (books, movies, TV, whatever) is so massively enriched and improved by cross-referring it with the experience of reviewers. As soon as I close the last page of a book, I jump online and read what other people have said about it. I love to read what cleverer or better informed or just different minds to my own think about the shows and paintings and songs that I've experienced too. I find it weird that anyone might think otherwise."

He concedes that the impact of reviews on an artwork's success is murky: "Whether reviews matter in terms of an artwork's success or failure (and who gets to define that?!) is less clear. Depends on the show. Depends on the circumstances. At any rate, reviewers are part of an ecology that responds to the art and entertainment that gets put out into the world, and one of the many factors that may influence how those artworks are received, understood and savoured. And the world would be more drab and undistinguished without them. (But then, I would say that…)"

So as the Fringe kicks off, remember: the stars are arbitrary, the reviews are subjective, and somewhere a critic is probably sighing at the thought of another poster with four stars plastered on it. But hey, at least the shows are good.