Extra word in the sentence: I'm sorry, but I have to finish my term paper today.

[Runs1215]

A: Tim, may I borrow your laptop this afternoon?
B: I'm sorry, but I have to finish my term paper today.

May I know why the word "but" is needed in the answer given by B?
It seems to me that the meaning is the same even without the 'but'...

is it matter if extra words (with no meaning) appears in the sentence?

[Mister Micawber]

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'But' is not necessary, but it is useful; it is one way for the speaker to make a refusal more gradual, more conciliatory, and more roundabout.
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Native English teacher at Mister Micawber's

[Yankee]

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In addition to what MM wrote, the word 'but' also serves as a conjunction in that sentence.

Yes, those "extra" words can often make a big difference in how the listener perceives a sentence.
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"Nearly all men can stand adversity, but if you want to test a man's character, give him power." ~ Abraham Lincoln

[Runs1215]

I see, thx ^^

[Nessie]

So 'but' is not necessary? why? I agree with Amy that 'but' is a conjunction in this case, and so without 'but' we have 2 sentences ('I'm sorry' and 'I have to finish my term paper today') with no link? It's wrong, isn't it?
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:(... something we never have again, I know... I guess I really really know.. :(

Sorry seems to be the hardest word...

[Yankee]

Hi Nessie

I would recommend always including the word 'but', especially in more formal English.
It can be omitted in informal English. However, excluding it does tend to make the sentence sound more abrupt, and therefore not as nice/polite, in my opinion.
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"Nearly all men can stand adversity, but if you want to test a man's character, give him power." ~ Abraham Lincoln