Be supposed to

[JaneGothic]

I am studying the construction "be supposed to". It is mentioned that it has different meanings:
1. To be expected to do or be something
2. Used to say what someone should do

But I don't understand the difference between them. For example, Merrian Webster Dictionary provides this sentence for the second meaning: You are supposed to listen to your parents.

I thought when someone says what we should do, should possesses this meaning of expectations from other people. So I don't really understand why these 2 meanings are separate from each other here

 

[emsr2d2]

One is an expectation and one is something that you are (sometimes legally) obliged to do.

We're supposed to be going to my parents' house on Sunday. (It's a plan and, barring unforeseen events, you'll go.)

You're supposed to wear your ID pass round your neck at all times when on work premises. (This is a rule and you're expected to follow it.)

 

[jutfrank]

So I don't really understand why these 2 meanings are separate from each other here

I strongly agree that these should not be understood as two separate meanings. Rather, both attempt to describe the same core deontic sense of expectation, either by external obligation or by social norm, or some mix of the two.

You are supposed to listen to your parents = This is what you are expected to do, partly because of the cultural norm of society, and partly because it's what your parents oblige you to do.

Which book are you studying? Are you referring only to Merriam-Webster? If so, I'd urge you to use a different reference.