Se usan estos verbos para describir conclusiones o suposiciones.
You must be insane to jump off a moving train.
should / ought to
He should be here in five minutes. / She ought to have bought the cabbage.
This can only be Pete driving like a maniac in our backyard.
They could be still at work or they could be in the bar next door.
She may have left already, but I can't tell for sure.
This might be the wrong way we are going.
It is seven o'clock, he will be arriving at New York just now.
Al usar el indicativo se presentan los hechos como más
bien probables, al usar el subjuntivo se presentan como
más bien improbables. Con complementos circunstanciales
de tipo maybe, possibly, it's likely,
it is certain, I'm sure, if I'am right también
se pueden expresar conclusiones o suposiciones.
I assume they are at the theatre.
He presumed that she was at the hairdresser's
She guessed we were at the bar next door.
Maybe he went to the shop to get some milk.
They possibly got lost on the way to here.
if I'm right
She didn't go to school, if I'm right (if my feeling is right etc.)
if I'm not mistaken
If I am not mistaken, I would say that he has broken a leg.