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.

Rereading Candide, I was struck by the link between optimism and the optimal, the idea that we have been placed in this optimal world rather than some other.

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.

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.

Theatre within theatre, when characters sees themselves on stage, always raises philosophical questions of choice and free will.

Also, everyone thinks they know Candide - you hear people described as 'Panglossian'. So if Candide appears on a poster, it feels familiar.

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 .