Censorship of books did not start with the Vatican's Index, as claimed by Tim Graves, curator of Sussex University's Subversion And Censorship exhibition (Argus, May 10). It has always existed.

The first Chinese emperor, in 213 BC, ordered the destruction of all books except agricultural and medical manuals. For good measure, 460 writers of books were buried alive. In ancient Athena, the works of Protagoras were burnt and the author banished because he wrote he did not know whether there were truly gods or not.

The remnants of the great library at Alexandria were destroyed in AD 641 by Muslim invaders on the grounds that if its books contained statements contrary to the Koran they were evil, and if they agreed with the Koran they were redundant. Masses of books were destroyed during the Reformation and the Inquisition.

One important factor about subversive or offensive works is the matter of context. Hitler's Mein Kampf has a historical context. Salman Rushdie's Satanic Verses has a literary and cultural context. Change the context and an offensive work may no longer be so, while an inoffensive one may become one.

Pornography may be fine in a pornographic bookshop but unacceptable on a street hoarding. Hitler's book may be offensive at a Nazi rally but a dull tome in a university library. Rushdie's novel is dynamite in Iran but a yawn here.

Political correctness tends to destroy diversity of context. It wants either pornography on every hoarding or none anywhere. It finds Mein Kampf on a library shelf as offensive as at Nuremberg. And, I have to say, this exhibition, which places Mapplethorpe and Lawrence, Hitler and Swift, cheek by jowl in its exhibition cases, may well be doing the same thing.

-Graham Chainey, Marine Parade, Brighton