It is also used in short answers with the same meaning of think/believe/imagine/expect. Note that two forms of the negative are possible here:
- Will Jeremy be at Peter's this evening? ~ I don't think/suppose/imagine/expect so.
- Will you try to see Jennifer when you get back? ~ I think/suppose/imagine/expect not.
- Would you be prepared to stay on for an extra week? ~ I suppose/expect/guess so.
Note that suppose here describes a mental or emotional state, and it is not normally used in the continuous form.
以上是 BBC Learning English 中的解释。另外，British Council - English Grammar中也有类似的说法：
Suppose and supposed to are used very frequently in British English too. We shall see that suppose has a number of different meanings and uses and that supposed to is different again from suppose.
suppose = think/believe/imagine/expect
In this sense, suppose is often used in requests with negative structures when we hope the answer will be positive:
- I don't suppose you could lend me your dinner jacket, could you? ~ Sure! When do you need it?
- I suppose it's too late to see the doctor now, isn't it? ~ Hold on. Let me see if I can fit you in.
- I don't suppose I could see the doctor now, could I?~ I can fit you in at 11.30. Can you wait till then?
Google Trends 现在不能用，否则用它来查一查使用的普遍程度和趋势，会很有帮助。
Searching "I don't suppose so" returned "About 668,000 results"，所以，还是有很多人用的。但也有人说用的人越来越少了，或较少听到。
04 Jul '14, 22:29