Enlightenment is man's emergence from his self-imposed nonage.
Nonage is the inability to use one's understanding without another's guidance. This nonage is self-imposed if its cause lies not in lack of understanding but in indecision and lack of courage to use one's mind without another's guidance. Sapere Aude! Dare to Know! Have the courage to use your own understanding is therefore the motto of the Enlightenment.