How often have you been quite certain about something, only to discover that what you believed wasn't true, that you were in fact mistaken or even completely wrong?

Maybe, as a child, you thought as I did, that all dogs were male and all cats were female. I once read about a teenager who believed her brother when he told her that all bank notes are made from dolphin skin; that's why, he said, bank notes feel different to normal paper. Someone else thought that laughter tracks on TV comedy shows were actually the sounds of other people laughing in their homes all over the country, being broadcast ‘live’. She used to sit near the TV and laugh loudly so she could hear herself on TV. And someone else I read about described how, when she was little, she was terrified of getting on high-speed trains. She stood on the platform while they screamed through the station and assumed that it was like that inside the train, too.

Maybe you once discovered that the lyrics you'd been singing for years were, in fact, completely wrong. Someone I once knew was surprised to discover that the lyrics to Blondie's chart-topping hit ‘Denis’ were not, as she'd been singing, ‘beneath the knees’ but ‘Denis Denis’. And someone else told me they thought that a line in Queen's ‘Bohemian Rhapsody’ was ‘Saving his life from this warm sausage tea’. The correct lyric? ‘Spare him his life from this monstrosity’.

Ridiculous? Yes. Yet when it comes to your own thoughts about yourself, other people and the world, you probably believe they are all rational and valid. It rarely occurs to you that your thoughts about events might be illogical, unreasonable or just plain wrong!

How, then, can we be certain that anything we think or believe is true? There is, after all, always more than one way of thinking about yourself, other people, events and situations.