Exprimer une conviction
I'm sure / certain (that) he's ill.
Je suis sûr / certain qu'il est malade.
I feel quite sure that… Je suis pratiquement sûr que…
I am convinced that he knows the answer.
Je suis convaincu qu'il connaît la réponse.
It's obvious / Obviously he has lied.
C'est évident, il a menti.
There's no doubt about it.
Il n'y a aucun doute là-dessus.
I'm in favour of / opposed to… Je suis pour/contre…
Exprimer un doute
I'm not quite sure about the answer.
Je ne suis pas très sûr de la réponse.
I'm not convinced about the result.
Je ne suis pas convaincu du résultat.
It's not at all certain that…
Ce n'est pas du tout certain que…
I can't say for certain but… It's difficult to say for certain…
Il est difficile de dire avec certitude…
I have doubts about… J'ai des doutes sur…
There is an element of doubt about…
Il y a un doute au sujet de…
listen!
Allison to her best friend…
Allison: “Obviously Tom didn't tell me the truth about his weekend.”
Jessica: “I can't say for certain but he has never lied before.”
Allison: “I'm not convinced at all about his explanations! I now have doubts about everything he says.”