Change your opinions, keep to your principles; 

change your leaves, keep intact your roots.

Every dogma has its day.

Rascals are always sociable, more's the pity! 

and the chief sign that a man has any nobility in his character 

is the little pleasure he takes in others' company.

Learn from your dreams what you lack.

Every philosophy is tinged with the colouring of some secret imaginative background, 

which never emerges explicitly into its train of reasoning.

By denying scientific principles, one may maintain any paradox.

The greatest happiness 

of the greatest number 

is the foundation of morals and legislation.

To make your children capable of honesty is the beginning of education.

A lie would have no sense 

unless the truth were felt dangerous.

There is nothing so strong or safe 

in an emergency of life 

as the simple truth.

Your mind will answer most questions 

if you learn to relax 

and wait for the answer.

Explorers have to be ready to die lost.

I must have something to engross my thoughts, 

some object in life which will fill this vacuum, 

and prevent this sad wearing away of the heart.

There can be no happiness 

if the things we believe in 

are different from 

the things we do.