Recently, John McIntyre posted a video in which he defended the unetymological use of decimate to the Baltimore Sun’s Facebook page. When he shared it to his own Facebook page, a lively discussion ensued, including this comment:

Putting aside all the straw men, the ad absurdums, the ad hominems and the just plain sillies, answer me two questions:
1. Why are we so determined that decimate, having once changed its meaning to a significant portion of the population, must be used to mean obliterate and must never be allowed to change again?
2. Is your defence of the status quo on the word not at odds with your determination that it is a living language?
3. If the word were to have been invented yesterday, do you really think “destroy” is the best meaning for it?
…three questions!

Putting aside all the straw men in these questions themselves, let’s get at what he’s really asking, which is, “If decimate changed once before from ‘reduce by one-tenth’ to ‘reduce drastically’, why can’t it change again to the better, more etymological meaning?”

I’ve seen variations on this question pop up multiple times over the last few years when traditional rules have been challenged or debunked. It seems that the notions that language changes and that such change is normal have become accepted by many people, but some of those people then turn around and ask, “So if language changes, why can’t change it in the way I want?” For example, some may recognize that the that/which distinction is an invention that’s being forced on the language, but they may believe that this is a good change that increases clarity.

On the surface, this seems like a reasonable question. If language is arbitrary and changeable, why can’t we all just decide to change it in a positive way? After all, this is essentially the rationale behind the movements that advocate bias-free or plain language. But whereas those movements are motivated by social or cognitive science and have measurable benefits, this argument in favor of old prescriptive rules is just a case of motivated reasoning.

The bias-free and plain language movements are based on the premises that people deserve to be treated equally and that language should be accessible to its audience. Arguing that decimated really should mean “reduced by one-tenth” is based on a desire to hang on to rules that one was taught in one’s youth. It’s an entirely post hoc rationale, because it’s only employed to defend bad rules, not to determine the best meaning for or use of every word. For example, if we really thought that narrower etymological senses were always better, shouldn’t we insist that cupboard only be used to refer to a board on which one places cups?

This argument is based in part on a misunderstanding of what the descriptivist/prescriptivist debate is all about. Nobody is insisting that decimate must mean “obliterate”, only observing that it is used in the broader sense far more often than the narrower etymological sense. Likewise, no one is insisting that the word must never be allowed to change again, only noting that it is unlikely that the “destroy one-tenth” sense will ever be the dominant sense. Arguing against a particular prescription is not the same as making the opposite prescription.

But perhaps more importantly, this argument is based on a fundamental misunderstanding of how language change works. As Allan Metcalf said in a recent Lingua Franca post, “It seems a basic principle of language that if an expression is widely used, that must be because it is widely useful. People wouldn’t use a word if they didn’t find it useful.” And as Jan Freeman has said, “we don’t especially need a term that means ‘kill one in 10.’” That is, the “destroy one-tenth” sense is not dominant precisely because it is not useful.

The language changed when people began using the word in a more useful way, or to put it more accurately, people changed the language by using the word in a more useful way. You can try to persuade them to change back by arguing that the narrow meaning is better, but this argument hasn’t gotten much traction in the 250 years since people started complaining about the broader sense. (The broader sense, unsurprisingly, dates back to the mid-1600s, meaning that English speakers were using it for a full two centuries before someone decided to be bothered by it.)

But even if you succeed, all you’ll really accomplish is driving decimate out of use altogether. Just remember that death is also a kind of change.