1) I request you to attend my letter as soon as possible, in earnest.

2) I request you to attend my letter as soon as possible in earnest.

3) I request you, in earnest, to attend my letter as soon as possible.

The context for the above is a letter sent by a client requesting about one of our products. My question is the placing of the words in earnest. Which is the correct?

Your thoughts please.
Hello, Andrei Emotion: smile

The different positions of "in earnest" may change the meaning of the sentence.

First of all, the sentence should be better if it said "I request you attend...", without "to".
Also, "attend to my letter"; not "attend my letter".
Attend means 'to be present at' or 'to go to' when it is not followed by "to".

Sentences #1 and #2 seem to be similar. "In earnest", as I understand it, would mean that the client expects you to pay serious attention to their letter.
In sentence #3, the client seems to be saying that they are serious about their request.

But it isn't always easy to "guess" what people mean when they use adverbials that have great mobility within the sentence. Some people write something and they are not aware that they have not written what they meant.

Hopefully, someone else will post a better response to this.

Take care,

I see two ways of writing this sentence that would be grammatically and stylistically acceptable:

1. I request, in earnest, that you attend to my letter as soon as possible.
2. I request that you attend to my letter as soon as possible, and in earnest.

[1] and [2] have slightly different meanings. In [1], it is the client who is earnest (in making this request). In [2], the client is requesting that you be earnest in handling his request.

For future reference, I don't suggest that you use the phrase "in earnest" in sentences like these. In my opinion it sounds a little silly.
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Thanks for the reply. It was a stupid mistake by me to write 'attend my letter'. It should be 'attend to my letter'.

Attend to something or someone means give some careful thoughts.

Well, I hope the others will comment too. I am a bit perplexed by your interpretation of the three sentences.
 taiwandave's reply was promoted to an answer.
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I don't think I've come across "in earnest" more than a couple of times in my life.
Why do you say it's "silly"? Is it an old-fashioned expression? Does it sound a bit too pompous?

Thank you.