First, they can be used when we want to say how sure we are that something happened / is happening / will happen.
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What is the grammatical form ,function and meaning of "how" here?
Jigneshbharati What is the grammatical form ,function and meaning of "how" here? It denotes how certain the speaker is about the idea. For example 'must' denotes logical certainty here: It's snowing, so it must be very cold outside.
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JigneshbharatiWhat is the grammatical form ,function and meaning of "how" here?
It denotes how certain the speaker is about the idea.
For example 'must' denotes logical certainty here:
It's snowing, so it must be very cold outside.
Here, the use of 'could' denotes not a certainty but a possibility:
I don't know