A little confused,asking people if they would like to do something...
My workbook has just taught me that to ask if someone would like to do something I must use a negative question: Koohii wo nomimasenka.

It is a little confusing why it isn't: Koohii wo nomimasuka ?

If I was to use 'koohii wo nomimasuka', would it mean something different?

Question

A little confused,asking people if they would like to do something...
My workbook has just taught me that to ask if someone would like to do something I must use a negative question: Koohii wo nomimasenka.

It is a little confusing why it isn't: Koohii wo nomimasuka ?

If I was to use 'koohii wo nomimasuka', would it mean something different?

Answer

If I'm asked "Koohii wo nomimasuka?," the person may want to know if I have coffee regularly or if I like coffee.
If I'm asked "Koohii wo nomimasenka?," the person invite me to have some coffee.

Answer

Thanks everyone... you have given me some good insight :)

Answer

Yeah it's confusing.
Some textbooks just say that a negative form makes a sentence more formal.
You will see such an expression in a Japanese exam.
So both of them are correct.

In my opinion, if someone says "koohii wo nomimasuka", the person doesn't know whether you want it, thus you can decide if you take or refuse it. On the other hand, if someone uses the negative question, the person suggests it to you and expects you will take it.

Answer

Strictly speaking, I think `koohii wo nomimasuka` is not correct.
'koohii wo nomimashouka' is more correct.

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Though I'm not very sure for my English, I think the difference is like "let's go to the movie" and "why don't we go to the movie?". The actions of these sentences are the same, aren't they?