In this sentence, is "must" expressing probability or certainty? Why?
"Now you must be wondering, what causes this?"
When it does not express obligation, 'must' expresses logical deduction. You must be wondering ... ~ I, the speaker, deduce through logic that, from what I have said so far, you are wondering (what causes this).
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When it does not express obligation, 'must' expresses logical deduction.
You must be wondering ... ~ I, the speaker, deduce through logic that, from what I have said so far, you are wondering (what causes this).
In other words,
You must be wondering ... ~ The only reasonable conclusion I can draw from the facts so far is that you are wondering (what causes this)