Our friends show us what we can do; our enemies teach us what we must do.

Certain flaws are necessary for the whole. It would seem strange if old friends lacked certain quirks.

All theory, dear friend, is gray, but the golden tree of life springs ever green.

Science arose from poetry... when times change the two can meet again on a higher level as friends.

Someday perhaps the inner light will shine forth from us, and then we'll need no other light

Our senses don't deceive us: our judgment does