When something happens unintentionally, do you say “by accident” or “on accident”? “I deleted the report by accident” and “I deleted the report on accident” both sound OK in conversational English, but only one is technically correct. According to a grammar authority (English professor Paul Brians at Washington State University), “on accident” is a nonstandard, colloquial phrase, and the correct version is always “by accident.” But why?
While the prepositions “by” and “on” can both make sense in these phrases, “by” is the historical source of the expression. According to the Oxford English Dictionary, “by accident” is a direct translation of the Middle French phrase par accident (meaning “by chance”), an adaptation of the earlier Latin phrase per accidens, which emerged around the fourth century. “On accident” showed up in English around the 19th century, but for traditional grammarians, it’s still the nonstandard choice.
Nearly two decades ago, Indiana State University linguistics professor Leslie Barratt did a deep dive into why “on accident” is infiltrating English grammar. Younger participants, born in the 1990s, almost exclusively used “on,” while older participants, born in the 1970s and earlier, used “by.” Those born in the middle used a mix of the two. Why this shift occurred was unclear to Barratt, but one leading theory is that “on accident” mimics the structure of its antonym, “on purpose,” providing a kind of linguistic symmetry.
While Barratt’s original research observed a decline in the use of “by accident,” in the 20 years since the study, “by” has seen a resurgence. Looking at the lifespan of “by accident” using Google Ngram, we can see a steadily declining trend from 1800 through the late 1990s. However, in the early 2000s, “by” picked up momentum, and usage has been increasing ever since. “On accident” usage reveals interesting patterns, too. The phrase was rarely used from the 1800s through the early 1900s, until it saw a sharp uptick during the 1910s, reaching its peak around 1935. It then slowly declined until around 2010, when it started to increase in popularity again. Today, both prepositional phrases are gaining momentum in contemporary English.
These fluctuating trends prove that grammar norms are constantly changing — but will our style guides and grammar school lessons account for these shifts? It seems they haven’t yet caught up with “on accident.” For now, stick with “by accident” in formal writing and settings, but feel free to use “on accident” in casual conversations, so long as you aren’t speaking with an English teacher.
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