If untraditional grammar drives you around the bend, I suggest you steer clear of automobile ads this season. In particular, you'll want to take a detour to avoid Mercedes-Benz's tagline for the 2012 C-class coupe: "More power. More style. More technology. Less doors." And for your own safety, please pull over to the shoulder if you chance upon an ad for the 2012 Honda Civic that proclaims "To each their own." You don't want to risk the road rage.

Calmer now? Good. Because I'm going to use the rest of this column to take a closer look at these mischievous slogans and at "bad" ad grammar in general.

First, let's review the infractions in question. As you no doubt know, Mercedes breaks the grammar rule that says "less" is used with mass nouns and "fewer" with countable nouns: less money, fewer dollars; less weight, fewer pounds. "Door" is a countable noun; ergo, we're obliged to say "fewer doors." Meanwhile, Honda breaks the rule about singular and plural noun/pronoun agreement: "each" is singular, but "their" is plural. Ergo, "to each their own" should be "To each his own."

Ergo, the Mercedes and Honda copywriters are guilty of (a) ignorance compounded by (b) carelessness with an overlay of (c) pandering to the lowest common denominator.

Not so fast.

As someone who's spent my professional life in and around advertising, I can assure you that the writers responsible for these ads are in command of the English language, are fully aware of the rules, and broke them intentionally. Ad writers do this all the time: their goal, after all, is to make you stop and pay attention, and word play, word invention, and — yes — unconventional grammar are time-honored ways of accomplishing that end. (For other examples, see my columns on the Hanes Lay-Flat Collar and on "Rethink Possible" and "Think Different.")

Copywriters also count on the Pareto principle, sometimes called the 80/20 rule: 80 percent of people who encounter the "bad" grammar either won't recognize it as "bad" or will recognize it and not care. (They may even see it as a positive attribute.) Only 20 percent will object strongly enough to raise a fuss (the Honda ads exhibit "tragically bad grammar"; the Mercedes campaign represents "language malpractice"), and that fuss will simply serve to draw more attention to the campaign.

But let's take this a little further. You and I may indeed have been taught that the rules about less/fewer and singular/plural are inviolable. (I know I was.) But it turns out they aren't. Not only that: the rule-breakers have a lot of history on their side.

Take "less doors," Mercedes's way of telling customers that the new model is a coupe rather than a sedan. The 2002 edition of Merriam-Webster's Dictionary of English Usage (MWDEU) observes in a long entry that"less" and "fewer" were for centuries interchangeable. ("Less" was used for countable objects by, for example, King Alfred the Great in the 9th century.) Then, in 1770, a language writer named Robert Baker expressed a mild preference for "fewer" in certain cases. "No Fewer than a Hundred appears to me not only more elegant than No less than a Hundred but more strictly proper," he wrote. MWDEU's editors express a certain bemusement: "How Baker's opinion came to be an inviolable rule we do not know." Well, not 100 percent inviolable: we're comfortable enough saying "the car has less than 60,000 miles on the odometer" and "that's one less thing to worry about." And yet "less doors" strikes some people as odious. Would "fewer doors" sound better? Not to my ear.

As for the singular "their" in "to each their own," there's plenty of honorable precedent for that usage, too, going back to Jane Austen ("Who makes you their confidant?") and even further back to Chaucer ("And whoso fyndeth hym out of swich blame,/They wol come up..."). They were finding a way around our lack of a common-gender singular indefinite pronoun — in English, unlike French or Spanish, we're stuck with he or she, his or her. In the 18th century, when the logicians got their hands on English grammar, it was decreed that singular masculine pronouns were always to be used in indefinite expressions: "Will everyone remove his hat?" (The logicians were all men.) Today, in an attempt to be fair and nonsexist, we often substitute "he or she" and "his and her," but those phrasings can be awkward, especially in ad copy. MWDEU quite reasonably observes: "The plural pronoun is one solution devised by native speakers of English to a grammatical problem inherent in that language — and it is by no means the worst solution."

So does this mean I approve of the Mercedes and Honda ad campaigns? Actually, no — but my objections aren't grammatical ones.

In the case of Mercedes, I consider "less doors" to be inconsistent with the company's brand image, which is polished and upscale. Yes, the C-class coupe is priced lower than other models, but it's still classified as an "executive car." "Less doors" would sound appropriately colloquial in an ad for, say, a Chevrolet pickup. But it's grating in copy for a brand that stands for luxury, sophistication, and high performance.

(Compare, for example, the long-running slogan for Gund, the makers of cuddly stuffed animals: "Gotta Getta Gund." The nonstandard spellings are perfectly suited to the brand's informal, child-pleasing personality.)

Mercedes had another option, one that would have sounded catchy yet would have broken no rules. Mignon Fogarty (Grammar Girl) put it succinctly in a comment on her own post about the campaign: "They could have simply said 'less door' instead of 'less doors.'" That's the ad line I'd have chosen.

As for Honda, the problem here is that "To Each Their Own" riffs on a well-known idiom — "to each his own" — that goes all the way back to Cicero's "Iustitia est unicuique suum tribuendi" ("Justice is the giving of each to his own"). (And no, the soundtrack for the Honda ads isn't "To Each His Own.") The change to "their" is neither clever nor brand-enhancing; it just sounds dumb, and "dumb" isn't an adjective we want to associate with a carmaker. How to fix it? Well, Honda might have gone with "To Each Its Own," which makes sense with the weird-characters theme. It could matched each ad's featured character with a gendered pronoun — "To Each Her Own" for the lady ninja, for example. That approach would have emphasized the personalization angle Honda is pushing. But frankly — and I speak here as a longtime Honda owner as well as a verbal-branding critic — the whole campaign seems off-target — and off-putting — to me. I'd go back to the drawing board on this one.

But that's just my opinion. The Honda slogan has its defenders: "It's clear what it means, and that's the important thing," wrote a reader at The Inspiration Room. And read the comments on Grammar Girl's post about "less doors" to see some well-reasoned defenses of that usage: "It's a stronger rhetorical play," wrote one commenter. Which just goes to show: with advertising, as with driving, your mileage may vary.