Learners' Questions: Using 'suppose' and 'supposed to'

Sanmati from India says: People use 'suppose' and 'supposed to' a lot of the time in conversation. Can you please tell me in which sense and where they should be used?
Dan has the answer. Watch the video and do the exercise here:
Transcript
Hi guys! Dan here for BBC Learning English with this week's Learner Question. Find out what it is after this.
OK! This week's learner question comes from Sanmati from India, who writes: People use suppose and supposed to a lot of the time in conversation. Can you please tell me in which sense and where they should be used? Ok, Sanmati. Here we go.
So, suppose can mean think, believe, imagine or expect, and in this sense, suppose is often used with negative structures when we hope the answer will be positive. For example: I don’t suppose you could lend me £20, could you?
It is also used in short answers with the same meaning of think, believe, imagine, or expect, and note that two forms of the negative are possible. For example: Do you think he will be late? I suppose so. I suppose not. I don’t suppose so.
Now, suppose and supposing can also be used in a completely different way to mean something like ‘what if’. And this is to introduce suggestions or to express fear. Now, note that the verb which follows suppose or supposing can be in the present tense or the past tense. So, for example: Suppose I come tomorrow instead of Friday, will that be ok? Or: Supposing I came tomorrow instead of Friday, would that be ok?
We can also use the structure be supposed to plus the infinitive. And this means that something should be done because it is the law, the rule or the custom. However, in practice, it’s probably not done. For example: I’m supposed to clean my room before I go out, but I never do!
Finally we can use the expression supposed to be to mean generally believed to be true by people. For example: This medicine’s supposed to be good for stomach cramps. Why don’t you try taking it?
Finally, when you use supposed to in speech, note that the ‘d’ is not pronounced. It is pronounced suppose to. However, when you write it down, don’t forget the ‘d’, ok?
I hope that answers your question Sanmati. Thank you very much for writing to us. If anybody else out there has a question for Learners’ Questions, you can email us on: [email protected]. Please remember to put Learners’ Questions in the subject box and your name and where you’re writing from. We get a lot of emails, guys. I’m afraid we can’t answer every single one of them, but we do read them all. And for more information, go to our website bbclearningenglish.com. That’s it for this week’s Learners’ Questions. I’ll see you next time. Bye!