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There was once a beggar who had tried many ways to get money. At last he thought
he would pretend to be dumb. Now one day a gentleman who had known the beggar by
sight
passed by. He went up to the beggar and asked him suddenly :“How long have you
been dumb?” The beggar was taken by surprise and quite forgot that he was ‘dumb.’
He answered quickly :“Oh, ever since I was born,sir.”

*********

The underlined part, how about "knew the beggar by sight"? Is it also allowable?
Comments  
Yes; I like that much better. 'Had known' is wrong there: it indicates that the man no longer knew him by sight.
Hi. I am somewhat not sure why "had known" indicating cessation of having known the beggar by sight is the only reading you can get. (I am not sure I wrote correctly to reflect what I wanted to say, though) Could we also read into it and derive an interpretation that says "he had known the beggar upto that 'one day' he passed by"?

pructus wrote this to ask his question:

There was once a beggar who had tried many ways to get money. At last he thought
he would pretend to be dumb. Now one day a gentleman who had known the beggar by
sight
passed by. He went up to the beggar and asked him suddenly :“How long have you
been dumb?” The beggar was taken by surprise and quite forgot that he was ‘dumb.’
He answered quickly :“Oh, ever since I was born,sir.”

**

Now let me write like this, not creating similar context all the way, but about the half the way (of what pructus wrote. Please read it and answer the question that follows it. Thank you for your anticipated help.

There was once a professional tennis player. One day, he thought he would pretend to be not so professional and thus not so good at tennis. Some time later, in a tennis match with his distant cousin, a friend who had played with him in some professional matches happened to pass by, and struck a conversation ...

Question: Does the use of past perfect, "had played," indicate the friend's ceasing of playing tennis matches with the professional tennis player? I don't think so. I think it indicates his having had some professional matches with the professional tennis player up to the moment of his strucking the conversation.
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'Had played'in past matches is fine; they are no longer playing. However, as I have already said, you cannot suddenly not 'know the beggar by sight'. The beggar looks no different now. Hence, no past perfect.
Thanks a lot, Mister Micawber!!
Hi,

I feel that you figure that the "had known" is not incorrect there. You are saying that it is also an option. I guess you are saying that "had known" is used to indicate "the gentleman who had known the beggar up to that time". Have I understood you?
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This is a reply to the post above by Anonymous.
I see.... There was a reply by Mister Micawber... And I understand his explanation. There is a difference between doing some matches and knowing some one.