Critics are important - even in the blogosphere - Telegraph We all have opinions about what we see; we can spend a lot of time arguing about our varying views, and now we have infinite cyberspace in which to do so. The fact that I disagree with you doesn't make me a good critic and you a bad one - it doesn't make us critics at all. A critic is someone who devotes their time to the pursuit of cultural judgement. They don't exist simply to give a thumbs up or down. The best critics use their knowledge and judgement to analyse something they have seen, to set it in context, to give us guidance on what it might feel like. Because this is a hard craft to master, they are still likely to work for newspapers or magazines or established online organisations that can afford to pay them for their opinions. They will very likely be writers whose words give pleasure - and who help the reader to understand the sphere in which they write. As a teenager, I learnt about ballet by reading critics such as the late John Percival, and Clement Crisp who described performances and productions in a way which both brought them to life and linked them to a historic tradition. This is part of the role of the serious critic, as a brilliant new app from the V&A makes clear. Played In Britain: Modern Theatre in 100 Plays, 1945-2010 puts each of its theatrical milestones in context, with introductory remarks, original cast lists, photographs and contemporaneous reviews from the Telegraph and the Guardian. What's fascinating is that these instant judgements - against the individual's own taste sometimes - are generally so sound. Take Look Back in Anger, from 1956. Kenneth Tynan's grandstanding cry of "I could not love anyone who did not wish to see this play" is the one we all remember. Yet both the Telegraph and the Guardian's critics recognised John Osborne as a distinctive new voice, while disliking some of the play's more self-indulgent qualities (verdicts that look more sound with time). When Mark Ravenhill's Shopping and F***ing opened exactly 40 years later, both papers took a sharp intake of breath at the sheer brutality of what my fellow panellist depicted. Michael Billington called him "an uncontrolled talent" while Charles Spencer hailed the play as "a revolting but persuasive portrait of our times." He concluded: "[Its] harsh neon-lit poetry, the savage humour and scenes of disgusting degradation throb in the memory like an unlanced boil." This is theatrical history being written on the run: passionate and incisive. Could a blogger consistently produce the same level of authority and care? Time will tell, but until then I believe that the vibrancy of cultural debate needs citizens who have opinions and critics who try to put their opinions at the service of the bigger picture. And we shouldn't confuse the two. The app, Played in Britain, is available now from iTunes Read other columns by Sarah Crompton here