When a scientist doesn't know the answer to a problem, he is ignorant. When he has a hunch as to what the result is, he is uncertain. And when he is pretty darn sure of what the result is going to be, he is in some doubt.
Richard P. Feynman (2011). “"What Do You Care What Other People Think?": Further Adventures of a Curious Character”, p.263, W. W. Norton & Company
