I doubt whether this is true (or not).
Every one is at liberty to doubt whether ... (or not).
I do not doubt that (i. e., I am sure that)...
Who can doubt that...?
It is as if a man should doubt whether he has a head on his shoulders.
Can we imagine any man seriously doubting whether...?
She found herself wondering at the breath she drew, doubting that another would follow.Meredith.
I am afraid that you will become so afraid of men's motives as to doubt that any one can be honest.Trollope.
There is nothing for it but to doubt such diseases exist.H. G. Wells.
I do not think it would have pleased Mr. Thackeray; and to doubt that he would have wished to see it carried out determines my view of the matter.Greenwood.
That the movement is as purely industrial as the leaders of the strike claim may be doubted.Times.
And I must be allowed to doubt that there is any class who deliberately omit...Times.
He may doubt that his policy will be any more popular in England a year or two hence than it is now.Greenwood.
I doubt the correctness of the assertion... I doubt, I say, that Becky would have selected either of these young men.Thackeray.
But that his army, if it retreats, will carry with it all its guns ... we are inclined to doubt.Times.
It was generally doubted that France would permit the use of her port.Times.