Which era within history do you consider to be the most important historical period for ideas (for example, the golden classical age, the renaissance, the age of reason, or the twentieth century)?
I've a predilection for remote antiquity: human's minds have hardly changed in 150,000 years and I suspect our ancestors had thought of just about everything that really matters by twenty or thirty thousand years ago. The way most of us think nowadays - values, styles of thinking, intellectual priorities - was laid out by sages of two to three thousand years ago. In my book the reader is a third of the way through before even getting to Classical Greece, where most histories of ideas start. But it's vital to remember that historical periods don't really exist - they're just historian's devices for classifying material. So there are no real differences. There are times, places and networks that seem extraordinarily productive - China of the Hundred Schools, Classical Athens, Quattrocento Florence, Enlightenment Edinburgh - but I wouldn't call any of them particularly 'important' because importance is a relative term. Important to whom? For what? If by 'important' one means influential, the oldest ideas come top: they've had longest to register their influence.

Is there an idea or historical period (which generated particular ideas and concepts) that you are personally interested in?
To write this kind of book you have to suffer from severely undisciplined interests. The ideas that interest me most I haven't yet thought of. The most interesting history probably hasn't yet happened.

Which ideas do you consider to be the most important for those alive today to consider?
If they're alive they ought to be able to ask themselves what life is. The idea of a distinction between life and non-life is the starting point of most thinking about morals - which is what most people need to think about.

Finally, if you could name the idea that you consider to be the most pivotal in terms of the development of humankind, what would it be?
I don't think humankind has developed very much. We're as deficient in virtue as ever. So you're asking me what's pivotal to what's trivial. But the biggest breakthrough in the history of thought was probably the idea that reality includes more than mere matter. People now think materialism is terribly sophisticated and scientific - but really it is a glaringly obvious assumption. It took genius to challenge it. The idea that non-matter exists may, of course, be false. We can't test for it satisfactorily. But it's pivotal in the sense that once people have thought of it, the world never looked the same again. It liberated minds to re-imagine reality.