Whoever, in the pursuit of science, seeks after immediate practical utility may rest assured that he seeks in vain.

The originator of a new concept finds, as a rule, that it is much more difficult to find out why other people do not understand him than it was to discover the new truth.

Natural forces are measurable only in the form in which we know them, and the measure of their effect is energy.

All things are ungraspable.

-- Pyrrho

Color exists by convention, sweet by convention, bitter by convention; in reality there are only atoms and void.

-- Democritus

I know that I know nothing.

-- Socrates

You must learn all things: both the steadfast heart of well-rounded Truth and the opinions of mortals, in which there is no true trust.

-- Parmenides

For thinking and Being are the same.

-- Parmenides

Imagine prisoners chained underground since childhood, seeing only shadows on a wall and taking them for reality.

-- Plato