Sure, I meant "must be" in the colloquial sense of "I have a suspicion", not "I am absolutely certain". Like "it's 5pm, must be a lot of traffic on the highway

Sure, I meant "must be" in the colloquial sense of "I have a suspicion", not "I am absolutely certain". Like "it's 5pm, must be a lot of traffic on the highway right now". If traffic turned out to be light I would be mildly surprised, update my assumptions and move on with my life.