I should have understood because I myself come from a long line of occasional Johns. My first name, like my father’s, like his father’s, is John, but only in hospital, on ceremony or in school reports. The rest of the time we are called something else. I’m Richard, for example. When my father was ill the nurses called him John. Tell them your real name, I said. But he wouldn’t. I like it when they call me John, he said. It proves they don’t really know me.

Some of my pupils understand how he felt. They keep themselves at a distance, hiding under a false identity. So Robin might really like being Robin; it’s his special name, the one he gets at home. But at school he’s the commoner Robert.

Once when I visited my father in hospital, there was an old man in the next bed trying to get up. He was struggling with his trousers, so we drew the screens to give him privacy.

Suddenly there was a flap, a sound like an old clothes horse falling over, and a hand flopped under the curtain. I was the first on the scene. “Are you all right, sir,” I asked. I had this instinct to give him back the dignity he’d just lost. But my efforts were wasted.

The nurses came racing out of their pantry. “We’ve told you before, Ebenezer,” they shouted. Come to think of it, I’m not sure it was Ebenezer, but it was one of those wrinkly names that sound on nurses’ lips like something out of Dickens.

See what I mean about not letting on, said my dad, and I could tell from his smile that his neighbour had a secret name.

I take your point John, I said. And yours, Rob. And all the rest who prefer to use another name. My students call me Richard. I like that. But then I’m not on the floor, with my trousers down. I don’t need sir. Not yet.

Richard Hoyes teaches at Farnham College in Surrey.