I want to say that I did something a few months ago and I don't remember whether I've done that.
Which one should I say?
- I don't think I did something.
- I don't think I do something.
- I think I didn't do something.
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Sign up to join this communityFirstly, I think you already know this, but you should replace something with a more specific word or phrase:
- I don't think I did that.
Let's look at each sentence in turn:
- I don't think I did that.
I don't think I left the door unlocked [a few months ago].
This is the most common way to express this thought. "I don't think" is present tense and "I did that" is past tense.
- I don't think I do that.
I don't think I leave the door unlocked.
"I don't think" is still present tense and now "I did that" is present tense, which indicates habitual action.
- I think I didn't do that.
I think I didn't leave the door unlocked [a few months ago].
This could be either a once-off event, or habitual action in the past. If it is interpreted as habitual action, it implies that it used to be that case but it has changed since:
I think I didn't leave the door unlocked [a few months ago], but I think I do leave the door unlocked now.
So your best choice is #1, followed by #3 but #1 is much clearer than #3. #2 means something different from what you want to say.