Assuming something is true:
* "Presumably, the meeting will start at 9 am, but it's always best to double-check." (This assumes the meeting will start at 9 am, but isn't certain)
* "She didn't answer her phone, so presumably she's busy." (This assumes she's busy, but doesn't know for sure)
Expressing a likely reason:
* "The store was closed, presumably because of the holiday." (This suggests a likely reason for the store being closed)
* "He walked quickly, presumably to catch the bus." (This suggests a likely reason for his quick walk)
Showing uncertainty:
* "Presumably, this is the right address, but I'm not entirely sure." (This shows that the speaker isn't entirely certain about the address)
* "Presumably, they'll be back tomorrow, but we can't be certain." (This shows that the speaker isn't sure about their return)
Remember that "presumably" implies that you're not absolutely sure about something. It suggests a likely reason or outcome, but not a definite one.