Brilliant deduction

I was at the post office this afternoon trying to track down the mail I asked to be held while I was on vacation. Two others were in the same boat when I was there, and when I spoke to the manager, it was clear he'd had a lot of practice getting his rap down.

His best guess: With so many people in my building asking for vacation stops, and with the post office always so busy during the Christmas rush, "I deduct that it was probably human error."

How wonderful if he could deduct human error. I'm sick of blaming bureaucracy and bad luck -- I want a villain! But I kid. He meant "deduce," not "deduct."

Didn't he?

Well, yes, but it's not that simple. At the beginning, those words used to be fairly synonymous.

As you might guess, "deduce" and "deduct" both derive from the same Latin ancestor (deducere, to lead down or draw away). They also entered English at about the same time (early 15th century), and it was a while before people felt like they needed to differentiate. It makes sense in light of that Latin definition: You can take away an inference from facts, and you can take away a part from a whole. Not precisely the same idea, but our language has always been as creative as it is accommodating.

It's hard for modern ears to accept "deduce" for "deduct," but you'd think we would see the other mix-up all the time. (Especially since the noun "deduction" inconsiderately matches up with both verbs: "Sherlock Holmes had awesome powers of deduction, and maybe after this blog post I can use my movie ticket as a tax deduction.") Indeed, even though the modern distinction between "deduce" and "deduct" has been in place for ages, the usage of "deduct" for "deduce" is recognized in both the American Heritage Dictionary and Princeton's WordNet.

But in the latest edition of Garner's Modern American Usage, Bryan A. Garner calls "deduct" creep a Stage 1 language change, the lowest on his five-stage scale. If Stage 1 were a car, it would have three wheels.

That's a long way for a word to fall in 600 years.