It was enough to make a man doubt the existence of any higher celestial Power.

Foreign computer experts say they have seen no evidence of the virus, and some even doubt its actual existence.

No one doubted the tribe's existence up to the beginning of this century.

He has been unable to find such a document and doubts its existence as reported.

You've never seen a neutrino, but you don't doubt their existence.

After this, who can doubt the existence of miracles in the nineteenth century?

I am not one to doubt the existence of a sixth, or even sixteenth, sense.

By this time, however, Yockerbow was beginning to doubt their existence.

When her schoolmates doubt his existence, she has to produce him.

I've heard of him, but I have always doubted his existence.