Verbs for speculating

For speculating, guessing or discussing possibilities...

Ø About the present, use could, might, may be.

Ø About the past, use could, might, may have + past participle.

For making deductions which you are very certain of...

Ø About the present, use must be/ can´t be

Ø About the past, use must/can´t/couldn´t have + past participle