It's doubtful that they have any serious political disagreements.
And I for one am doubtful that reducing the deficit or cutting spending alone will solve our economic problems.
I know that it is easy to lose sight of this truth—to become cynical and doubtful; consumed with the petty and the trivial.
This kind of doubtful, questioning, view of the Syrian troubles is surprisingly widespread here.
It is doubtful, though, whether these measures will be any more effective than they have been in the past.
"I don't doubt it at all," said the doubtful Dromedary to everyone's surprise.
In the broad pathways of the ocean such a chance is doubtful.
We might run down to the light-house by mid-day, while it is doubtful if we could reach the town until to-morrow morning.
It is doubtful if she would have realized its significance, had she seen it.
This, I fear, is a doubtful blessing, for it leads to a vast number of the birds being taken prisoner.