Everyone who observes himself doubting observes a truth, and about that which he observes he is certain; therefore he is certain about a truth. Everyone therefore who doubts whether truth exists has in himself a truth on which not to doubt.... Hence one who can doubt at all ought not to doubt the existence of truth.
…a lady of what is commonly called an uncertain temper --a phrase which being interpreted signifies a temper tolerably certain to make everybody more or less uncomfortable.