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Hi Alphe,

I would like to clear the doubts,

#1 On Seeing my friend, I greeted him.
#2 Seeing my friend, I greeted him.
 In the first sentence, the underlined one modifies the verb 'greeted'
In the second sentence, the underlined one modifies the subject 'I'
Am I correct?
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No, both are sentence adverbials, complementing the entire main clause ('I greeted him').
Comments  
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When I was a small kid, I have been told that participles act as adjectives. 'Seeing my friend, I greeted him.' So I think 'seeing my friend' is an present participle and i think it modifies the subject 'I'. I am sure it is present participle. I need some more replies.

It is indeed a present participle, but an adjective ('an interesting book') is only one of its functions.

oh, yes, I got it. Thanks MM
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