How do you know anything at all? I bet you know a lot of things. You know what your name is; probably the day, and that right now you’re reading this sentence. Weirdly enough, the very fact that you’re reading it means that I know you’re reading it too, and the odd sensation you get as you realise that this is true, even though I’m writing this in early 2012 in my study, makes you feel uneasy. Don’t kill me for my sorcery. So we know a lot of things. But how do you know that you know? Is there any chance – any chance at all – that you’re wrong? Of course there is. Unless you are possessed of spectacular perspicacity, you might have occasionally mistaken the day when on holiday, or the date, when asked. I even – and I am far from proud of this fact – forgot my age for about six months, and had to be reminded by my mother. At least I had the rare sensation of feeling a year younger, instantly. And also an idiot.