Breakdown of Marco non risponde. Non potrà parlare.
non
not
Marco
Marco
parlare
to speak / to talk
potere
can, to be able to
Questions & Answers about Marco non risponde. Non potrà parlare.
Why does the Italian sentence use the future tense potrà when the English translation says "He must not be able to" (present)?
This is the epistemic future you are currently learning about! In Italian, the future tense isn't just for things happening later. It's frequently used to make a guess, an assumption, or to express probability about something happening right now. So, non potrà here actually means "he probably cannot" or "he must not be able to" at this very moment.
Could non potrà parlare also mean "he won't be able to talk" in the future?
Yes, grammatically it can. Without context, non potrà parlare could just be a normal future tense statement. However, because the first sentence is in the present tense (Marco non risponde), context tells us the second sentence is a guess about his current situation.
If I wanted to guess "He must not be talking" (instead of "He must not be able to talk"), would I still use potrà?
No. Potrà comes from the modal verb potere (to be able to / can). If you just want to guess that he isn't talking, rather than guessing about his ability to talk, you would put the verb parlare directly into the future tense: Non parlerà.
How could I express this exact same guess without using the future tense?
You could use a word expressing probability along with the normal present tense. For example, you could say Probabilmente non può parlare (He probably cannot speak) or Forse non può parlare (Maybe he cannot speak). Using the future tense is simply a very common, native-sounding alternative to express this.