Test-gunpowder-pudding driven development

I was rereading chapter 3, Systems and Illusion in Jerry Weinberg's excellent An Introduction to General Systems Thinking yesterday. On page 56-57 Jerry writes:

If I say: "The exception proves the rule" in front of a large class, there will be a division in understanding... Some will believe I have uttered nonsense, while others will understand "The exception puts the rule to the test"

I've read the book four times. I'm a slow learner but this time something clicked and I immediately understood the earlier passage:

...the exception does not prove the rule, it teaches it.

Jerry goes on:

"Proof" in its original sense was "a test applied to substances to determine if they are of satisfactory quality."

I was struck by two thoughts when I read this. One was the parallel with testing. Of a test as a proof. The other was the word original. I realized that when I hear the word "proof" I have a strong association with its noun meaning rather than its verb meaning. I tend to think of a proof as a finished proof that completely proves something. It's the noun-verb thing I've blogged about before. I wondered if there were any old dictionaries online so I could get a feel for how the generally accepted meaning of the word proof might have changed over time. There is. http://machaut.uchicago.edu/websters has two Webster's dictionaries. The 1828 dictionary came back with:

Proof [noun] 1. Trial; essay; experiment; any effort, process or operation that ascertains truth or fact. Thus the quality of spirit is ascertained by proof; the strength of gun-powder, ...

The 1913 one came back with:

Proof [noun] 1. Any effort, process, or operation designed to establish or discover a fact or truth; an act of testing; a test; a trial.

and a modern dictionary http://www.thefreedictionary.com/proof said:

Proof [noun]. 1. The evidence or argument that compels the mind to accept an assertion as true.

I find the difference fascinating. The 1828 and the 1913 definitions define the noun as the process whereas the modern one defines the noun as the evidence resulting from the process.

Jerry continues:

We retain this meaning in the "proofs" of printing and photography, in the "proof" of whiskey, and in "the proof of the pudding." Over the centuries, the meaning of the word "prove" began to shift, eliminating the negative possibilities to take on an additional sense: "To establish, to demonstrate, or to show truth or genuineness."

At first I didn't understand the bit about "eliminating the negative possibilities". I think it's partly to do with my ITA spelling at school. But I am persistant. Slowly it came to me. The word that did it for me in...

"Proof" in its original sense was "a test applied to substances to determine if they are of satisfactory quality."

...was the word if. To determine if they are of satisfactory quality. The proof was an act. There was the possibility of failure.

I started thinking about the word proof a bit more. I googled the phrase "the proof of the pudding". If you think this phrase is pretty meaningless then you're right - it's a shortened version of:

The proof of the pudding is in the eating.

Again it's about the possibility of failure. It reminds me of the scene in the film The Cat in the Hat (another film Patrick and I love watching) where the Cat has just made some cupcakes (with the amazing kupcake-inator). He tries one and says:

"Yeuch. They're horrible. Who want's some?"

I love that line. I also googled the word proof as related to alcohol content. The history behind the phrase is just wonderful. In the 18th century spirits were graded with gunpowder. Imagine you're buying some spirits. How would you know if an unscrupulous merchant had watered it down? You couldn't tell just by looking. What they did was pour a sample of the solution onto a pinch of gunpowder. If the wet gunpowder could still be ignited then the solution had proved itself. Don't you just love that?

So let's hear it for pudding and for spirits and for gunpowder and for tests. And for the possibility of failure.


  1. The original overlap of 'proof' and 'test' as concepts and words is something I found out about a long time ago when I was flummoxed by the apparent illogic of "the exception proves the rule".

    If I recall correctly, it was my chemistry teacher at school who cleared up the history and distinction for me, by also pointing out "proof of the pudding", "proving ground" and "proof" in alcohol (yup, there's the link to chemistry).

    I also mention it occasionally when I talk about TDD. The original meaning of the word 'proof' still seems to be uncommon knowledge, particularly among programmers, whose domain is more obviously connected to mathematics than to cakes or chemistry.

  2. I also bumped into proving-ground - the place where the proving was done. Useful to have that as a separate place when gunpowder was involved I guess!

  3. The thing that throws a lot of people (including me) is that the expression is often used when an exception contradicts a rule. When used this way people imply that a rule is in some strange way made more valid by being incorrect in some cases.

  4. Yes. Now I know the origin of the phrase and how the meaning of the word proof has changed I feel I'd be better able to explain why its nonsense.

  5. Jon, you have proved to be an astute reader.

    I truly appreciate 20-proof readers like you.


  6. Jon, that was supposed to be 200 (two hundred) proof, not 20 proof.

    In other words, 100% alcohol, in that silly measurement system.

  7. Thanks Jerry. I nearly missed your use of "proved" in your first reply :-)

  8. I *knew* the cake was a lie!
    Now I have the proof.

  9. Anonymous4:20 pm

    The Oxford English Dictionary has citations back to 1200 for "proof" in the sense "evidence or argument establishing a fact." Maybe it became more common, but it certainly was not unknown in earlier times.

  10. And of course it is very hard to really know whether the noun-verb balance has truly shifted over time. I can really only speak for myself!