For what one has in black and white, One can carry home in comfort.

Thought expands, but paralyzes; action animates, but narrows.

Life belongs to the living, and he who lives must be prepared for changes.

Animals, we have been told, are taught by their organs. Yes, I would add, and so are men, but men have this further advantage that they can also teach their organs in return.

Every solution of a problem is a new problem.

No man learns to know his inmost nature by introspection, for he rates himself sometimes too low, and often too high, by his own measurement. Man knows himself only by comparing himself with other men; it is life that touches his genuine worth.

The human mind will not be confined to any limits.