Like everybody else, I have always been convinced that I have good days on which my ideas flow rapidly, my questions are sometimes sensible and my answers sometimes to the point. I also have bad days on which my body and mind are sluggish and even routine tasks get done badly, if at all. Now, in old age, good days seem rarer, and, when they happen, they no longer make everything magically easy. Is this just the lethargy of an under-exercised academic no longer paced by brilliant and energetic students and colleagues, or just another sign of aging of my mind?