When in doubt, don’t.

Benjamin Franklin

If the Sun and Moon should ever doubt, they’d immediately go out.

William Blake

There is no doubt that life is given us, not to be enjoyed, but to be overcome-to be got over.

Arthur Schopenhauer

And new Philosophy calls all in doubt, the element of fire is quite put out; the Sun is lost, and the earth, and no mans wit can well direct him where to look for it.

John Donne

I show you doubt, to prove that faith exists.

Robert Browning

Doubt is the father of invention.

Ambrose Bierce

Similarly, many a young man, hearing for the first time of the refraction of stellar light, has thought that doubt was cast on the whole of astronomy, whereas nothing is required but an easily effected and unimportant correction to put everything right again.

Ernst Mach

A conservative is someone who makes no changes and consults his grandmother when in doubt.

Woodrow Wilson

Any truth is better than indefinite doubt.

Arthur Conan Doyle

I no doubt deserved my enemies, but I don't believe I deserved my friends.

Walt Whitman

Test yourself on mankind. It is something that makes the doubter doubt, the believer believe.

Franz Kafka