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I have seen it happening/happen.

What is the difference?
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... have seen it happening. have seen the event unfolding, in progress before my eyes. I watched it as it was happening.
... have seen it happen. have seen the event occur in its entirety, to completion.

This difference is pretty much the same difference in any pair of sentences, one with a progressive (continuous) tense, the other with a corresponding simple tense.

Jane was walking home. (Focus on action in progress.)
Jane walked home. (Focus on the accomplishment of an action.)

I saw Jane walking home.
I saw Jane walk home.


CJ
Comments  
I have seen it happen many times at that intersection where people ran the red light which resulted in horrible accidents. [happening] does not work in this context here]

I actually saw the real estate downturn happening back in May 2006. Happening is used as a present participle to describe the direction of the market. -ok
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 CalifJim's reply was promoted to an answer.
CalifJim... have seen it happening. have seen the event unfolding, in progress before my eyes. I watched it as it was happening.
... have seen it happen. have seen the event occur in its entirety, to completion.

This difference is pretty much the same difference in any pair of sentences, one with a progressive (continuous) tense, the other with a corresponding simple tense.

Jane was walking home. (Focus on action in progress.)
1. Jane walked home. (Focus on the accomplishment of an action.)

I saw Jane walking home.
I saw Jane walk home.

CJ
Hi, CJ, I concur with you mostly except for the line in blue. If you view that as focus on the accomplishment of an action, then how do you depict the following sentence?

2. Jane has walked home.

Isn't it the actual focus on the accomplishment of an action? If yes, wouldn't it be better to describe sentence 1. as focus on a past action?

Excuse me for my intrusion.
No worries, Pioussoul.

"Without you mention/mentioning it, I will have done tit he other way."



Are both choices equally acceptable in this context? I have a feeling that this context can only take 'mention'.

Also, in the sentence below, "telling" sounds more appropriate. I can't explain Emotion: sad

"Without you tell/telling me, I will have done it the other way".
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Both Jane has walked home and Jane walked home focus on a past action and focus on the accomplishment of that action. The difference is a matter of current relevance, which is only expressed in the first of these.

My point was that there is a certain distinction between walked home and was walking home (both past), namely, that the focus is on the completed accomplishment and on the on-going performance of the walking home, respectively, and further, that this distinction is the same as the distinction between I saw her walk home and I saw her walking home, which are essentially: I saw this: She walked home and I saw this: She was walking home. (It would have been an unnecessary complication, as well as irrelevant, to introduce the idea that the first of these two could also have been given as I saw this: She has walked home.)

CJ