In Act 3, Scene I of Sheridan's The Critic, Dangle and Sneer are watching the rehearsal of Mr Puff's tragedy about the Spanish Armada, and he excitedly awaits the entrance of his 'principal character', Lord Burleigh: 'I only hope the Lord High Treasurer is perfect - if he is but perfect!' When I first read the play, I did not understand this line. The joke, I thought, lay in the disproportion between the modesty of Puff's tone and the impossibility of his wish. In fact, the real point soon becomes apparent. Lord Burleigh enters, goes through an elaborate series of facial expressions, but says nothing. 'Hush!', Puff warns, 'or you'll put him out.'

The joke, in other words, is based on the fact that the theatrical meaning of the word 'perfect' is 'word-perfect'. An actor is the sum of his or her lines, and a perfect performance is one in which these lines have been perfectly learned. It is the association of being wordperfect with other kinds of perfection that I want to explore in this article.

It seems, oddly enough, to be a new topic. Actors' lapses of memory are generally regarded in the same category as other technical hitches, like doors that do not close properly and offstage noises in the wrong place. It is an unwritten rule that theatre reviews ignore all but the most spectacular lapses on the opening night of a production. By contrast, you can hardly read any actor's biography or memoirs without coming across anecdotes about 'drying', most of them comic, some of them extremely implausible.