"On accident" (meaning "accidentally") does seem to be an unusual usage that frequently appears in opposition to the much more idiomatic "on purpose" (meaning "purposefully").
These are the kinds of idioms commonly used by e.g. children in explaining why something has gone wrong: —"You broke my toy on purpose!" —"No, it was on accident!".
A quick survey of the 34 incidences of "on accident" in the Corpus of Contemporary American English show about half have the sense discussed here, and "on accident" does occur in opposition to "on purpose": HAAS:
That happens in so many cases where you're got misinformation
that's either leaked on accident or on purpose.
— from "Gunman Kills 32, Wounds 28 at Virginia Tech" on On the Record w/ Greta Van Susteren on Fox News, 2007 JACOBUS:
Big difference when it's on purpose and when it's on accident.
— from "Dean, Democrats and Iowa's Deadline", on CNN, 2003 Other examples are from fiction:
"Dad better not see this or you'll get it.
I'll tell him we were play fighting, and I slugged you on accident.
" —
Evan Shopper, "If I have to hit one of you, I'll hit you both" in The Massachusetts Review , 2003
She was thirteen years old, called herself a "gangsta ho" even though all her friends were white, and had already dropped out of school.
"
On accident," she said - she'd broken her collarbone the year before horsing around on her cousin's dirt bike and missed so much school that she simply never bothered returning. — Emily Shelton, "From MEMPHIS (Short story).
" in Chicago Review , 2003 "By accident", in contrast, has 1419 results, making it more than 100 times more common, and occurring not just in spoken and informal written English, but also in formal edited writing in academic journals, magazines, and newspapers.
english.stackexchange.com/users/39/nohat
"On accident" sounds strange to me. "
By accident" sounds better, but I can't understand how it could be much different from "On purpose", albeit very strange to say "By purpose".
english.stackexchange.com/users/131/Dan
A quick Google search of "fell by accident" versus "fell on accident" suggests that "by accident" is used about 99% of the time.
But with "tripped by/on accident" there are more results for "on".
I've never encountered "on accident" until seeing this question, so I think it must be something peculiar to the US.
english.stackexchange.com/users/129/njd
He tripped on accident.
He was eaten by accident.
Those are the forms I would use, if forced to choose between them.
However, there is no grammatical difference between the two 1 , and I chose those because they "sound right" .
I don't believe there is actually a rule which states which to use, but I could be wrong about that.
This matter, of course, is solved if we use the word accidentally .
1
Yes, the second sentence is in passive voice, while the first is in active, but I don't think that's the root cause.
english.stackexchange.com/users/100/waiwai933
As the original question makes pretty clear, this is a change in progress (you see this kind of stratification by age all the time with changes in progress).
In the earlier stages of such a change, you can't expect to find it much in writing, so results from google, etc, are going to be misleading.
It's likely there is also regional variation here as well.
To me "on accident" (raised in northern California) is normal, though sounds slightly less formal.
As for why this might be happening, I like ShreevatsaR's theory.
english.stackexchange.com/users/78/Alan Hogue
In situations like these, I tend to lengthen out the phrase.
Replace "by" with "by way of
a/an" He tripped by way of an accident.
accident here adds information to the clause "he tripped" "Purpose" is something thought out, perhaps written down, requiring more formal thought.
A synonym for "purpose" is "intent".
He tripped by intent sounds better than "He tripped on intent".
Therefore, I would guess that although we are more comfortable with "tripping 'on' purpose" I wonder if "tripping by purpose" is actually a more accurate phrase.
In addition, "He tripped on..." could be followed by an object as well. "
He tripped on a cat" Sorry for the rambling.
english.stackexchange.com/users/134/OneProton
Both sound reasonable to my ear, though I like "by accident" better.
Doing some basic corpus analysis finds that "by accident" is much more prevelant.
The Corpus of Contemporary American English lists 1419 occurrences of "by accident" vs only 23 for "on accident".
A quick Google comparison gives 7,030,000 hits for "by accident" vs 1,020,000 hits for "on accident".
Interesting to be sure.
Perhaps this is in reference to Barratt's paper on the topic, and language change in general.
Changes like this do happen, and it isn't unusual for usage to be clearly defined by generations (consider the verb impact).
One conclusion drawn here is that people are seeking parallelism with "on purpose", though it also concedes that it's hard to know for sure.
english.stackexchange.com/users/89/Charlie
I have some friends in the south (Louisisana) who always say "on accident" and think "by accident" sounds wrong.
My friends in the North (New Jersey/Pennsylvania) think "on accident" sounds wrong.
It may be a regional thing, but I don't have enough data to say for sure.
english.stackexchange.com/users/111580/Keith
Usual fluent english usage would be "...
by accident" as distinct from "..
on purpose".
More elegant in prose would be "...accidentally"
english.stackexchange.com/users/43133/user43133
There is a great chasm on these phrases in the US.  The great divide seems to be currently centered at the age of 40.  The younger generation has began shifting to "on accident" for unknown reasons.  What is your view?
Is it correct to say "on accident" instead of "by accident"?
english.stackexchange.com
<word-choice><prepositions>
english.stackexchange.com/questions/215
english.stackexchange.com/users/12/Eruditass
"On accident" appears to be much less common than "by accident", although it may have come about as opposition to "on purpose". "By accident" is probably used about 99% of the time, although differences in usage may also be regional. In any case, it is not clear whether there is actually a rule to say whether one or the other is more correct. On accident' appears to have arisen from a mistaken comparison to 'on purpose'. It is far less commonly or less widely used and therefore may sound incorrect in formal texts.
"On accident" appears to be much less common than "by accident", although it may have come about as opposition to "on purpose". "By accident" is probably used about 99% of the time, although differences in usage may also be regional. In any case, it is not clear whether there is actually a rule to say whether one or the other is more correct. A google search will give hits that show "by accident", opposed to "on accident" is used 99% of the time. This could also be American English usage only. One conclusion drawn here is that people are seeking parallelism with "on purpose".
Although understandable, "on accident" is said to sound strange to many people, in favor of "by accident". This may be a regional difference. However, Google searches and other checks show that "by accident" us used the vast majority of the time. The exact answer to this question may depend on the regional dialect where you are. However, it appears that most people prefer "By accident" and indeed, most corpus studies show this to be signficantly more common.
On accident' appears to have arisen from a mistaken comparison to 'on purpose'. It is far less commonly used and therefore may sound incorrect in formal texts. By accident' sounds better. By accident' is far more common - 'On accident' must be US English - it is not used in UK English.. There is no rule for this. On accident' is a new form that is still not widely used. By accident' sounds better. In the southern US people say 'on accident' and in the north 'by accident'.
A google search will give hits that show "by accident", opposed to "on accident" is used 99% of the time. This could also be American English usage only. One conclusion drawn here is that people are seeking parallelism with "on purpose".
"By accident" appears to be the more approved term. Most corpus-analyses seem to demonstrate that "By accident" is used significantly more than "On accident". The difference in usage of "On accident" and "By accident" could be regional.