Doubt is an achievement. Invention rests on a foundation of doubt. Doubt, what we do not know, illuminates not only what is yet to be known but also what knowing is, its limits and what a wonder it is.

Doubt is more light than dark.

We turn to our doubts for relief from our beliefs as much as we turn to our beliefs for relief from our doubts.

Our doubts are most productive in the regions of our minds where we are most secure.

We are never more intimate with ourselves than in our self doubts.

Doubt is our deepest freedom. It has the peculiar characteristic that it may alternately brighten and darken the world we live, passing instantaneously and unpredictably from one to the other.

Realistic doubting is the antithesis of confusion.

Only the isthmus of doubt separates the sea of understanding from the sea of folly.