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.

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.

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'.

The American journalist Barbara Ehrenreich has written about this in her book Smile or Die: How Positive Thinking Fooled America and the World (2009) . She talks about the happiness industry, the rise of medication to make us happy and of self-help books, and the influence of all this on religion. In many ways religion has become another form of self-help. We all suffer from over-exposure to positive thinking.

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

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.

In the business world, the idea of positive thinking is absolutely entrenched.