@KaJe,
Quote: 1. [He can be here to ask us for something. (I think that he is likely here to…)
2. This can mean that… (This probably means that…)
First you have to understand what 'can/could' mean, KaJe. They both mean "something is possible [according to the speaker's mind]", but they don't really describe any particular range of possibility like 'might/may/should-likely-probably/must-almost certainly' do.
Let's take one example 'will'. This same range of certainty applies in the same fashion to all English lexical/semi-modal verbs - be, need to, want to, have to, go, eat, be able to, would, could, can, be about to, ... .
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Percents show the English modals/semi-modals used to describe a speaker's measure of certainty
100% will eg. He will go to London.
90-99% must/almost certainly eg. He almost certainly will go to London.
50.1% to 89% should/probably/likely eg. He likely/probably will go to London.
26-50% may eg. He may go to London.
1-25% might eg. He might go to London.
0% won't/will not eg. He will not go to London.
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Again, 'can' doesn't describe any specific range of certainty. It only says that something is possible. 'can' is not possible here in your example for this specific reason. In English, we do not use 'can' to describe actual one time realities which is what is being done in your sentence.
We use 'can' to describe general/permanent realities, eg.
It can rain there this time of year.
You can find milk over there in the dairy section.
This type of flour can be used to make pasta.
When denoting 'possibility' we do NOT use 'can' for a one time situation as in your sentence.
For your number 1 sentence;
1. [He can be here to ask us for something. (I think that he is likely here to…)
'can' is NOT possible, for the reason described above. To get the same nuance, we would use, 'could' -
1a.
He could be here to ask us for something.
This says the same thing as 'can' in the sense of "it is possible". Indeed we can paraphrase 1a. with,
It is possible [that] he is here to ask us for something.
If you wanted to say,
(I think that he is likely here to…), which denotes an over 50% to about 89% certainty,
He likely/probably is here to ask us for something.
If you wanted to say a 35% certainty,
He may be here to ask us for something.
If you wanted to say a 15% certainty,
He might be here to ask us for something.
If you wanted to say a 95% certainty,
He must be here to ask us for something.
OR
It's almost certain he is here to ask us for something.
If you wanted to say a 100% certainty,
He is here to ask us for something.
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I'll stop here for now because you likely/probably [51-89%] have some things puzzling you and you may [26-50%] want to ask some questions.