He who loves practice without theory is like the sailor who boards ship without a rudder and compass and never knows where he may cast.

The painter who draws merely by practice and by eye, without any reason, is like a mirror which copies every thing placed in front of it without being conscious of their existence.

He who wishes to be rich in a day will be hanged in a year.

He who is fixed to a star does not change his mind.

Science is the captain, and practice the soldiers.

Anyone who conducts an argument by appealing to authority is not using his intelligence; he is just using his memory.