I see these two expressions are used almost identically in different contexts. Is there a difference between I have got and I have gotten?
In general, "have got" is the present perfect form of "to get" in UK English, while "have gotten" is the US English version.
However, even in US English, "have got" is used in certain instances, namely to mean present tense have (in the sense of possession, or to mean must):
- I have got a lot of friends. (=I have a lot of friends)
- I have got to go now. (=I have to go now/I must go now)
Gotten is probably the most distinctive of all the AmE/BrE grammatical differences, but British people who try to use it often get it wrong.
It is not simply an alternative for have got. Gotten is used in such contexts as
They've gotten a new boat. (= obtain)
They've gotten interested. (= become)
He's gotten off the chair. (= moved)
But it is not used in the sense of possession (= have). AmE does not allow
*I've gotten the answer.
*I've gotten plenty.
but uses I've got as in informal BrE. The availability of gotten does however mean that AmE can make such distinctions as the following:
They've got to leave (they must leave)
They've gotten to leave (they've managed to leave).
I try to avoid the "have got" constructions whenever possible. Usually where you feel like saying "I have got" you could substitute the simpler "I have" and no one would be the wiser. Unless you're speaking informally and using got for emphasis, as in "I have got to get out of this place," you can usually just drop that got.
As for gotten, I see no harm in using it informally in sentences like "I have gotten quite good at archery," although if you want to speak more formally you could say "I have become quite good at archery." Still, who would use the latter when boasting about archery prowess in a bar?