A basic tenet of the court system, going back to British common law, is that a suspect is “innocent until proven guilty.”

A basic tenet of grammar is that that tenet is ungrammatical.

The Associated Press Stylebook, The New York Times Manual of Style and Usage, and The Chicago Manual of Style all tell us to use “proved” as the past participle of “prove.” “Proven,” they say, is an adjective.

As is often the case, we’re not listening.

“‘He’s really proven himself to be a great utility guy for this football team,’” one citation said. “Education has proven to be a great source of urban success,” said another. And here’s someone who wants it both ways: “Indeed, the youth programs have proved a useful adjunct in making books a year-round habit for many kids … Over the years, summer reading programs have proven to be a win-win undertaking.”

No one seems to get the immediate past tense of “prove” wrong: it’s “proved.” But many, many people believe that the next step back, the past participle—the form that is combined with “to have” or “to be”—is “proven.” Why this is so is not clear, but could arise from a misunderstanding: The past participles of many irregular English verbs end in “en”; the past participle of regular verbs, of which “prove” is one, end in “ed.”

Merriam-Webster’s Dictionary of English Usage traces the first “misuse” of “proven” for “proved” to 1829, and says: “Surveys thirty or forty years ago show proved to be about four times as common as proven. But proven has caught up in the past twenty years” and is now “about as common as proved as part of a verb phrase.”

Garner’s Modern American Usage holds the ramparts, saying “proven often ill-advisedly appears” as the past participle, even as it ranks “proven” at Stage 4 on the Language-Change Index, meaning the battle is all but lost.

“Proven” is a perfectly good adjective: A candidate “has a proven record of fighting against tax increases.” But, as sometimes happens, people will use “proved” as the adjective instead: “It is also the leading Appalachian gas producer, with proved reserves of 2.9 trillion cubic feet.”

M-W is inclined to acquit any use of “proved” or “proven,” calling the interchangeability of them as past participle or adjective “standard now.”

Is that wrong? It will depend on whether you follow one of the Big Three style guides or the common habit. But if you are called on it, you can be proven innocent by usage guides. Unless, of course, you make someone “innocent until “proved” guilty. Then you’re guilty of ignoring idiom—probably a misdemeanor.

Merrill Perlman managed copy desks across the newsroom at The New York Times, where she worked for 25 years.