Great are those two gifts, wisdom and continence: wisdom, forsooth, whereby we are formed in the knowledge of God; continence whereby we are not conformed to this world.
Saint AugustineEveryone 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.
Saint Augustine