Isaac Newton didn’t invent the cat door.

There’s an urban legend bouncing around the internet that says Isaac Newton invented the cat door. In the book Dirk Gently’s Holistic Detective Agency, Douglas Adams had one of his characters heaping praise on Isaac Newton for inventing the “cat flap”. But a lot of things were fictionalized in the book. For example, it says Isaac Newton attended St. Cedd’s College, which is a fictional school. Plus, the character who makes the claim could have been mistaken, or lying. And it’s very likely that Douglas Adams was misinformed, or simply making stuff up.

Here’s one fact we do know. There was a house in England which had two cat doors cut into the kitchen door, one large and one small. Someone claimed that Isaac Newton used to live in that house.

That’s it. That’s all the facts to support the theory that Isaac Newton invented the cat door. There’s no patent with his name on it, no contemporary news articles, no mention of it in his numerous biographies written in different centuries.

There was a person who pointed at the two cat doors in a house which used to belong to Isaac Newton and said that Isaac Newton must have not been very smart because a smart person would have realized that it was pointless to cut two doors, one large and one small, and a smart person would have known that one large hole would have been good enough. This person imagined that Isaac Newton had a mama cat and a kitten so Isaac decided to cut a small hole for the kitten and a large hole for the mama. Ha ha ha. That’s so funny I forgot to laugh.

In fact, you can easily imagine the joke went like this…

Those college boys think they’re so smart. Well, I tell ya, they ain’t so smart. I once knew a college boy who was so dumb, he had a mama cat and a kitten so he cut two cat doors, one big and one small. He thought he was smart and he knew all kinds of stuff from books but when it came to common sense, he was dumb. And that college boy’s name was [fill in the blank with anyone who is famous for being smart].

The joke works equally well with Einstein if you’re an American, Newton if you’re British, or Rene Descartes if you’re French.

But the joke only works if you assume that the audience listening to the joke knows about cat doors.

If he invented the cat door, and it was a new invention, then nobody would be making jokes about how stupid he was for cutting two of them in the same door. People wouldn’t understand the joke unless they could relate it to their own experiences.

Of course, we have no proof that both holes were cut by the same person, let alone any proof that the person was Isaac Newton himself. It’s perfectly plausible that Isaac Newton hired a carpenter to cut a hole for a small cat and then a century later the new occupant hired a carpenter and said “That hole is too small for my big cat.” so the new carpenter cut a second hole, thinking that’s what the home owner wanted, and then the home owner yelled at him for not just making the first hole bigger. Then years later, someone blamed it on Isaac Newton. Then Douglas Adams wrote a book.