This book argues that the Stoics invented the concept of moral duty. Its author, Jack Visnjic, opens by admitting that this was not his original intention. Like many others, he accepted the predominant view that the notion of moral duty is a modern invention often associated with Immanuel Kant. Visnjic’s original plan, he tells us, was simply to examine the prehistory of this modern notion. However, his research led him to the view that the standard account is false.

When I opened this book, I did so as a firm believer in the standard view. The Stoics were no moralists telling people what they ought to do. They had no categorical imperative, only what Kant would have called a hypothetical imperative: if you want to enjoy a good life, then live consistently with Nature, virtue, etc. Visnjic’s book, then, is a head-on challenge to a central assumption in my own understanding of Stoicism and ancient ethics more widely. I was inevitably curious yet sceptical.