Last week on NPR's Morning Edition, sports commentator Frank Deford said in a piece about Serena Williams and her volatile style that "the proof is in the pudding." After a listener questioned the usage, I was called in to be the arbiter on the idiomatic expression. Is the proof in the pudding? Or is the proof of the pudding in the eating?

The way that Deford said it, as "the proof is in the pudding," is a common formulation these days, especially in American English. But it has morphed over the centuries from the original, "the proof of the pudding is in the eating." How did the shift occur? There were a couple of factors at work that led to the original form becoming veiled in obscurity. First of all, the words proof and pudding meant something a bit different when the saying first emerged. (The Oxford English Dictionary has examples with that approximate wording back to 1605.) Proof meant "test" — in other words, in order to know if your food is good to eat, you have to try it. By extension, the proverb came to mean that the way you judge the quality of something is in its practical use.

Pudding, meanwhile, didn't have anything to do with sweet, creamy desserts. Rather, in olden days, it could refer to a kind of sausage, with intestines of an animal, typically a sheep or pig, stuffed with minced meat and various other ingredients. As you might imagine, in the days before refrigeration this was a rather treacherous food, and something you'd want to try out carefully. (For more on the historical nuances of pudding, including its distinctions in British and American English, see Lynne Murphy's Separated by a Common Language blog.) 

Along with the changes in meaning of these two key words, the saying itself would often get shortened to simply, "the proof of the pudding" without the "eating" part. Take this line from To Kill a Mockingbird: "Judge Taylor might look lazy and operate in his sleep, but he was seldom reversed, and that was the proof of the pudding." With the original sense of testing out potentially dangerous sausage no longer obvious, it wasn't long before the elliptical version, "the proof of the pudding," morphed into "the proof is in the pudding." But if proof is understood to mean "evidence for something," then this new version doesn't make much sense if you stop and think about it. Why would we be looking for evidence hidden in pudding? Different people can find different rationalizations: my wife said it brought to mind the cliched "file in the cake" facilitating a prisoner's escape!

I don't fault Deford or anyone else for using the modern-day twist, "the proof is in the pudding," since the original is so opaque. (I note that even though "the proof is in the pudding" appears in the transcript of Deford's commentary, the online version has been changed to "the proof of the pudding is in the eating.") Proverbial language can sometimes be passed down from generation to generation with gradual misunderstandings akin to the Telephone Game. One wonders why this particular expression has held on, in mangled form, after the original meaning has slipped away. Perhaps it's the attractive alliteration of proof and pudding, combined with the iambic rhythm of "the PROOF is IN the PUDding." Sometimes the sonic qualities of a saying can be more important to its survival than its strict semantics.

You can listen to my explanation of the saying's evolution on NPR here.