Enlightenment is man's exodus from his self-incurred tutelage. Tutelage is the inability to use one's understanding without the guidance of another p… - Immanuel Kant

...[M]an and generally any rational being exists as an end in himself, not merely as a means to be arbitrarily used by this or that will, but in all his actions, whether they concern himself or other rational beings, must always be regarded at the same time as an end... [R]ational beings... are called persons, because their very nature points them out as ends in themselves, that is, as something which must not be used merely as means, and so far therefore restricts freedom of action (and is an object of respect).

Phenomena of the external sense are examined and set forth in physics; those of the internal sense in empirical psychology. Pure mathematics considers space in geometry and time in pure mechanics. To these is to be added a certain concept, intellectual to be sure in itself, but whose becoming actual in the concrete requires the auxiliary notions of time and space in the successive addition and simultaneous juxtaposition of separate units, which is the concept of number treated in arithmetic.

Enlightenment is man's emergence from his self-imposed immaturity. Nothing is required for this enlightenment except freedom; and the freedom in question is the least harmful of all, namely, the freedom to use with and publicly in all matters.