Enlightenment is man's emergence from his self-imposed immaturity. Immaturity is the inability to use one's understanding without guidance from another. This immaturity is self-imposed when its cause lies not in lack of understanding, but in lack of resolve and courage to use it without guidance from another.
Sapere Aude! [dare to know]
"Have courage to use your own understanding!"--
that is the motto of enlightenment.
An Answer to the Question:
What is Enlightenment? (1784)