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"I saw him to do it."

Is this sentence allowable, with a meaning, "I saw him when he was about to do it" OR "I made him do it by seeing him" = "He had to do it because I was watching him"
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pructus"I saw him to do it."

Is this sentence allowable, with a meaning, "I saw him when he was about to do it" OR "I made him do it by seeing him" = "He had to do it because I was watching him"

No. You need one of these:

I saw that he was about to do it. [similar to your first meaning]
I saw to it that he did it. / I made sure that he did it. [similar to your second meaning]

CJ
I see....

How about, "I saw him about to do it"?

Is this sentence allowed?
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Yes. That seems OK to me.

CJ
Thanks a lot, CalifJim...
the sentence is equal to the below one:
I saw what he did.
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Hi!

Could you give me a little more?

By "the sentence", you mean "I saw him about to do it." or "I saw him to do it."?