Optimism and happiness are not the same thing, but they are becoming interchangeable, and it seemed to me that Voltaire's Candide gave me a way into something important happening in modern-day culture.

Twenty years ago, when you bumped into someone and asked how they were, they would say, 'Mustn't grumble' or 'Getting by': now they feel obliged to say 'Just great!'. In both cases, the reply is just a social nicety, but the framework has changed, it's as if it's become a social duty to express happiness.

We are now so far advanced in our denial of evil that we want to rationalise it away.

There is a remarkable nimbleness of style, a balancing act of tone, in Voltaire, which is hard to bring off on stage. When you speak the words out loud, the effect is very different from when you read them. So one needs to do something new with a stage performance, not simply 'tell the story'.

Voltaire's novel [Candid] offers us parallel universes, the possibility of entering into alternative worlds existing side by side, and this is something quite modern. Nested narratives and parallel universes are popular at the moment in many different art forms.

I have not chosen to create a linear story, but a series of different narratives: in the end there are five plays that almost, but don't quite, add up to one play... I start with the story of Candide, being performed as a play within a play, to bring the audience up to speed with the story.

I have adapted the whole book [Candid] into tweets of 140 characters, and these are being sent out daily, at the rate of eight tweets per day .