One reason why columns like this are written is because so many writers don’t realize when a tautology has them in its grasp and won’t let go.

“Tautology” is a fancy word for “needless repetition,” or silly redundancy. And the first sentence in this column contains a double tautology. (Is that a duotautology?)

Evan Jenkins discussed separate pieces of the “reason” puzzle here more than ten years ago, dealing first with “the reason … is because.” “The sense of ‘because’ is already in the sentence in the word ‘reason,’” he wrote, “and if we use ‘because’ we’re repeating ourselves.”

Then he added an addendum (tautology intended) about “the reason why.” That “why,” he said, “rarely if ever serves a purpose.” “Reason” and “why” are virtually synonymous; why use both? (Apparently there are plenty of reasons. See below.)

In the intervening years, sodas and fries have been supersized, so why not phrases explaining causes? Not content to have merely “the reason why” or “the reason is … because,” people are adding them together:

“The only reason why teachers are teachers is because they’ve read more books on education than others.”

It appears frequently when people talk, but there’s no good reason for it to appear in prose outside of direct quotations, though it certainly does.

Someone who gives a “reason” is supplying a cause. “Because” supplies a cause. And “why” asks for the cause. It’s unreasonable to use a noun (“reason”), adverb (“why”), and conjunction (“because”) to explain one simple cause. Most English teachers would prefer that the phrase be rendered solely as “the reason … is that.”

“The reason … is because” and “the reason why” are both entrenched in English—Fowler railed against them in 1926, for all the good it did. Many usage guides simply sigh and accept fate. “We are not advising you to use the reason is because just because many well-known writers have used it,” Merriam-Webster’s Dictionary of English Usage says, but, if you do, “you will surely be in some very distinguished company.” Garner’s Modern American Usage puts “the reason … is because” at Stage 4 of the Language-Change Index, “ubiquitous but …”

As for “reason why,” M-W says it is less incorrect than many people believe, particularly college teaching assistants: “So if you are taking freshman English you had perhaps best avoid offending with this usage. Anyone else can use reason why freely.” Garner’s calls “reason why” correct, if idiomatic, and says it is “an unfortunate superstition that reason why is an objectionable redundancy.”

“The reason why … is because,” though, is another matter. It “is more common in older sources (it seems to have [can you double-check this quote and see if the words “been a” are supposed to be here?] favored construction of Swift’s) than newer ones but is certainly not yet extinct,” M-W says. Indeed, its use seems to be growing, perhaps fed by the extra time it gives one to phrase the cause. Even so, it’s a little bit like using a belt, suspenders, and a piece of rope to keep your pants up.

Let’s make it a cause, and limit reason to only one tautology per phrase. Because you can.

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Merrill Perlman managed copy desks across the newsroom at The New York Times, where she worked for 25 years. Follow her on Twitter at @meperl.