It is certainEs seguro
It is impossibleEs imposible
It is improbableEs improbable
It is not possibleNo es posible
It is not sureNo es seguro
It is not trueNo es cierto/No es verdad
It is obviousEs obvio
It is possibleEs posible
It is trueEs cierto/Es verdad
Not to be sureNo estar seguro
Not to believeNo creer
Not to denyNo negar
Not to doubtNo dudar
There is no doubtNo cabe duda de
There is no doughtNo hay duda de
To be sureEstar seguro
To denyNegar
To doubtDudar
to believeCreer