what should I consider must and have ?

"You must wipe your nose" implies an order and a person who is in a position to give such an order has authority over the person with the dirty/runny nose. "Wipe your nose or else."

"You have to wipe your nose" is a friendlier statement which simply states that a dirty/runny nose needs wiping.

I don't think there is any distinction between must, need to, or have to...

Or as Michael Lewis explains it:

'Have to' is objective necessity; 'must' is subjective necessity, the speaker's judgment of necessity.

I agree with Stu that here the differences among the three are negligible.

Well I have to disagree with Mr.Lewis; must certainly does not imply any subjectivity beyond the intrinsic subjectiveness of an opinionated statement, which would be equally present using any of the aforementioned words...

Are you referring only to the nose-wiping sentences in question, Stu, or do you think there is no distinction in any context?

I'm talking about the words in general!

With the WWW so handy, Stu, there's little excuse for fiats of the 'cogito ergo id est' variety. I am wondering, since the word choice is purely arbitrary, if any of the three (must, have (got) to, need to) can be used in these examples:

'She must be of a different breed; not many would throw away all that we fight for their job, not with eagerness.'

'You only need to read them each once. Except the last one, you need to read at least 3 times, and think carefully about each word, for it means so much.'

'I've got to hold on to you
when you are here

I've got to hold on to you
while you are still here
and I've got to hold on to you
when you are here'

'ultraviolet girl, I need your sunburn
and your skin, need to feel you
against my skin.'

-- Or is there some reason that the author made these choices (except for the meter in the case of 'must' of course)?

Sorry, I must have double-posted, so have had to delete one.

Hey, you found my poem thread! I thought had disappeared into the abyss many months ago.

I do think that any of the highlighted examples could be replaced with any of the others. The words I chose were chosen over the others simply because they came to mind or because of their pronunciation.

Certainly, the grammar around the sentence must be changed very slightly, but I do think that the meaning would be identical had the other words been used...

http://www.smic.be/smic5022/obligation2.htm

I found this, but this rule of thumb does not seem to apply in all cases and is therefore not really a distinction it would still be preference which is used..