‘Ages of liberty … are transitions, brave interludes between eras of custom and order,’ Will Durant wrote. ‘They last while rival systems of order struggle for ascendancy; when either system wins, freedom melts away. Nothing is so disastrous to liberty as a successful revolution; the greatest tragedy that can befall an ideal is its fulfilment.’ This is certainly the sense one gets from A C Grayling’s Towards the Light; liberty thrives in movement and stagnates in dozy tranquillity. Its habits are hard learnt and often counterintuitive; it is an effort to tolerate offensive opinions and hold firm to traditions in the midst of danger. It is a matter of urgency for every age to be reminded of why these traditions are vital.