Skepticism

It's not what we don't know that hurts: it's what we know that ain't so. 

There are similarities between absolute power and absolute faith: a demand for absolute obedience, a readiness to attempt the impossible, a bias for simple solutions to cut the knot rather than unravel it, the viewing of compromise as surrender. Both absolute power and absolute faith are instruments of dehumanization. Hence, absolute faith corrupts as absolutely as absolute power.

Life is doubt, and faith without doubt is nothing but death.

I respect faith, but doubt is what gets you an education.

Knowledge is an unending adventure at the edge of uncertainty.

It is important that students bring a certain ragamuffin, barefoot, irreverence to their studies; they are not here to worship what is known, but to question it.

Faith lives in honest doubt.

There lives more faith in honest doubt,
Believe me, than in half the creeds.

The authority of Plato and Aristotle, of Zeno and Epicurus, still reigned in the schools; and their systems, transmitted with blind deference from one generation of disciples to another, precluded every generous attempt to exercise the powers, or enlarge the limits, of the human mind.

Too bad that all the people who know how to run the country are busy driving taxicabs and cutting hair.

Skepticism, riddling the faith of yesterday, prepared the way for the faith of tomorrow. 

...the number of saintly men has not yet risen to the level where the census makes them a separate statistical category.

To know how to wonder and question is the first step of the mind toward discovery.