1. Temple of Urania, Georg Celer's frontispiece for Kepler’s Rudolphine Tables, 1627

2. Immanuel Kant, What Is Enlightenment? (1784) Enlightenment is man’s leaving his self-caused immaturity. Immaturity is the incapacity to use one’s intelligence without the guidance of another. Such immaturity is self-caused if it is not caused by lack of intelligence, but by lack of determination and courage to use one’s intelligence without being guided by another. Sapere Aude! (Dare to Know!) Have the courage to use your own intelligence! is therefore the motto of the Enlightenment.

3. Baron d’Holbach, System of Nature (1770) The enlightened man, is man in his maturity, in his perfection; who is capable of pursuing his own happiness; because he has learned to examine, to think for himself, and not to take that for truth upon the authority of others, which experience has taught him examination will frequently prove erroneous.