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I shouldn’t drink so much coffee at work. 
(Right)
6. Modals of Possibility & Probability – could, may, might, should, must, will, can
The Macmillan Dictionary says that possibility is the chance that something might happen or be true,
and that probability is a measure of how likely something is to happen.
This is probably the most common use of modal verbs, and all modals can express these two
functions in some way.
In terms of common usage, it is the 7 above that we are mainly concerned with here. We can order them
in this way:
Could, may, might ? maybe
Should  ? this is probably true
Must ? I’m pretty sure this is true
Will ? I’m very sure this is true
Can ? this is generally possible 
Remember that can is not used to talk about specific events:
Where's Paul? I'm not sure. He may / might / could be in his office. (NOT can!)
Here is another subtle difference between can and may / might / could:
Dogs can be dangerous. = Sometimes dogs are dangerous, but not usually
That dog may / might / could be dangerous. = it’s possible the dog is dangerous, we don’t know
for sure, be careful
We also use can't or cannot when we talk about things that are impossible (in our opinion):
That can't be true!
You cannot be serious!
We use must to say we are sure something is true and we have reasons to believe this:
It's getting dark. It must be quite late already.
You haven’t eaten all day. You must be hungry.
We use should when we want to suggest that something is true and we have reasons to believe this:
Ask my mother about that. She should know the answer.
It’s nearly 6 o’clock. The train should be here soon.
Last of all, we use will when we are quite sure that something is true because we know that this is how it
normally happens:
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