Many years ago I was sitting in a restaurant with a four-year-old boy. Like many or most four-year-old boys, he was intensely interested in vehicles of all sorts, especially the larger and louder ones. So when I heard a siren and saw something with flashing red lights go by, I said, "Look, there goes an ambulance."

He was already looking, naturally, and said "That's not an ambulance, it's a rescue truck."

In retrospect, I realized that it was stupid of me to argue with a four-year-old, but I was young and naive, and I persisted.

"No, it's an ambulance."

"No, it's a rescue truck."

"Are you sure? It looked like an ambulance to me."

He gave me a dark look and said "You have to compromise."

Surprised that he was using such a big and abstract word, I said "What does that mean?"

He gave me an even darker look.

"That means it was a rescue truck."