It is not only scientific knowledge that informs people’s preferences and determines how they choose to behave. There are also, for instance, moral criteria, which assign attributes such as ‘right’ and ‘wrong’ to possible actions. Such values have been notoriously difficult to accommodate in the scientific world-view. They seem to form a closed explanatory structure of their own, disconnected from that of the physical world. As David Hume pointed out, it is impossible logically to derive an ‘ought’ from an ‘is’. Yet we use such values both to explain and to determine our physical actions.
