[Grammar] the task of/for someone is to...

Hello. Two questions here.:-D

In an English assignment, one of the sentences I wrote was corrected in the following way, which I can't understand why:

[Original sentence]:
I think the top task for a psychoanalyst is to represent as many hidden wishes as s/he can.

[Corrected sentence]:
I think the top task of a psychoanalyst is to represent as many hidden wishes as s/he can.

1. Why changing for into of?
Could someone explain what using "for" here (and in general where "for" is appropriate to use) sounds like to you as a native speaker?

2. I'm always having troubles using prepositions accurately. Is there a book in which I could learn about them? Or is there a list on the Net for me to check the prepositions whenever I finish writing an essay?

Thanks a lot!:-D

NOT A TEACHER
I think your English teacher made a mistake there. Here are two examples taken from dictionaries.
"The task of the union representative is to fight on behalf of the members." <- This is from Longman (LDOCE5)
"a hard task for the committee" <- This is from Oxford (OALD8)

I find it a very odd sentence altogether. It's impossible to decide which is correct because neither one makes it a good sentence.

bhaisahab said:

I find it a very odd sentence altogether. It's impossible to decide which is correct because neither one makes it a good sentence.

Click to expand...

Hello bhaisahab, which parts seem odd to you? Can you get the general meaning from this sentence, or is it even impossible for a native speaker like you to understand what I was trying to express?
Thanks.

khanhhung2512 said:

NOT A TEACHER
I think your English teacher made a mistake there. Here are two examples taken from dictionaries.
"The task of the union representative is to fight on behalf of the members." <- This is from Longman (LDOCE5)
"a hard task for the committee" <- This is from Oxford (OALD8)

Click to expand...

Just to make sure I have the right understanding.
So when I use "of," I'm emphasizing the ownership, and when I use "for," I'm emphasizing the personal definition of the task, right?

azhu said:

Just to make sure I have the right understanding.
So when I use "of," I'm emphasizing the ownership, and when I use "for," I'm emphasizing the personal definition of the task, right?

Click to expand...

It depends on the situation. In this one, they are the same to me. Only native speakers can differentiate such subtlety, in my opinion.

bhaisahab said:

I find it a very odd sentence altogether. It's impossible to decide which is correct because neither one makes it a good sentence.

Click to expand...

Would the sentence sound better to you if I paraphrased it like below?
In my opinion, a psychoanalyst's most important task is to help the patients understand their various hidden wishes as much as possible.
NOT A TEACHER

azhu said:

Just to make sure I have the right understanding.
So when I use "of," I'm emphasizing the ownership, and when I use "for," I'm emphasizing the personal definition of the task, right?

Click to expand...

Not so in my opinion. Both prepositions work for me, and I cannot decipher any difference in meaning between the two.

khanhhung2512 said:

Would the sentence sound better to you if I paraphrased it like below?
In my opinion, a psychoanalyst's most important task is to help the patients understand their various hidden wishes as much as possible.
NOT A TEACHER

Click to expand...

That's much better.