One of my Facebook friends mentioned the usage I seen in very unfavourable terms. Unfortunately, what might have been an interesting linguistic discussion got sidetracked, partly by my fault.
Without a doubt, I saw is standard English and I seen is not standard English, but its usage is widespread in some varieties of English, so it can’t be dismissed out of hand. Most commenters online are immediately very unfavourable, some in most unhelpful terms. Of the few that provide an extended discussion, Anatoly Liberman of the Oxford University Press Blog starts by calling it “substandard but ubiquitous in conversational English”, and Patricia T O’Conner and Stewart Kellerman of the Grammarphobia blog note that it is heard “in much of the US, as well as in England, Scotland, and Ireland” (to which I would add Australia), and quote the Dictionary of American Regional English, which calls it “widespread” in the US, “esp freq among rural speakers and those with little formal educ.”
The development of features of non-standard varieties of English is, by the very nature of non-standard varieties, difficult to trace, but Liberman traces I seen to a reduced form of I have seen, alongside I (have) been and I (have) done. (In general, US English uses present perfect less than British English does. In fact, Liberman traces this first to Irish English.)
There are very few verbs for which this is even possible, and even fewer for which it actually happens. It’s plain not possible with regular verbs (talk-talked) or irregular verbs like put-put-put and say-said-said, for which the past simple and past participle forms are the same. This leaves only irregular verbs like beat-beat-beaten, come-came-come, go-went-gone, see-saw-seen and begin-began-begun. But no-one says (or vanishingly few people say) I beaten you yesterday or I come here yesterday. There is, especially, a very strong constraint against multi-syllable words being used in this way.
Realistically, the only verbs for which this happens are be, see, do, maybe go and the ‘i-a-u’ group (begin, drink, ring, sing, sink, swim), of which the three most common are Liberman’s been, seen and done. These are, incidentally, three of the most common verbs in English (first, eleventh and third on one major list of word frequencies (go is tenth)). (The use of I begun etc is more likely to be a simple mistake, though note “We’ve no less time to sing God’s praise Than when we first begun“.)
Wikipedia’s article on Southern American English includes I done and I seen along with done as a past tense auxiliary verb: I done told you before. Southern American English is spoken in a wide band across south-eastern and south-central USA from the Atlantic Coast to Texas, by at least millions of speakers, though, as Wikipedia says “increasingly in more rural areas and primarily by White Southerners”. My Facebook friend lives right on the edge of the shaded area on Wikipedia’s map.
Unfortunately, many statements disfavouring a particular form found in a particular variety of English come with a generous helping of judgement against the people who use that variety of English, including gender, age, location, perceived intelligence, perceived education and perceived socio-economic. (Note that I say “many”, not “most” or “all”, and that I don’t know my Facebook friend’s motivation.)
I don’t like I seen and its companions. I would never use them, unless to deliberately evoke a particular variety of English, and only then with caution. I would unhesitatingly correct any student who said or wrote it in class. But I would not ‘correct’ a native speaker of English whose variety just happened to include it, especially if I was visiting their part of the English-speaking world, and I wouldn’t use it even then. I speak like me; they speak like them.
Do people who say I been, I seen and I done not know that it is non-standard and so disfavoured, or do they not care? Do they decide to say these things? Possibly the conscious or subconscious influence of the people around them is stronger than what they learn at school or hear or read in the media. I speak very close to standard Australian English, so this doesn’t arise for me.
Language is never pure and rarely simple.
PS
A: “Who was that lady I seen you with last night?”
B: “You mean ‘I saw.'”
A: “OK, who was that eyesore I seen you with last night?”
Never Pure and Rarely Simple 