The whole interest of my reason, whether speculative or practical, is concentrated in the three following questions: What can I know? What should I do? What may I hope? (Critique of Pure Reason

All our knowledge begins with the senses, proceeds then to the understanding, and ends with reason. There is nothing higher than reason.

Enlightenment is man's release from his self-incurred tutelage. Tutelage is man's inability to make use of his understanding without direction from another. Self-incurred is this tutelage when its cause lies not in lack of reason but in lack of resolution and courage to use it without direction from another. Sapere aude! 'Have courage to use your own reason!'- that is the motto of enlightenment.

Skepticism is thus a resting-place for human reason, where it can reflect upon its dogmatic wanderings and make survey of the region in which it finds itself, so that for the future it may be able to choose its path with more certainty. But it is no dwelling-place for permanent settlement. Such can be obtained only through perfect certainty in our knowledge, alike of the objects themselves and of the limits within which all our knowledge of objects is enclosed.

...Reason should take on anew the most difficult of all its tasks, namely, that of self-knowledge, and to institute a court of justice, by which reason may secure its rightful claims while dismissing all its groundless pretensions, and this not by mere decrees but according to its own eternal and unchangeable laws; and this court is none other than the critique of pure reason itself.

...[N]ature generally in the distribution of her capacities has adapted the means to the end... [so nature's] true destination must be to produce a will, not merely good as a means to something else, but good in itself, for which reason was... imparted to us as a practical... absolutely necessary... faculty.

...[R]eason of itself, independent on all experience, ordains what ought to take place, that accordingly actions of which perhaps the world has hitherto never given an example, the feasibility even if which might be very much doubted by one who founds everything on experience, are nevertheless inflexibly commanded by reason; that, for example, even though there might never yet have been a sincere friend, yet not a whit the less is pure sincerity in friendship required of every man...

Simply to acquiesce in skepticism can never suffice to overcome the restlessness of reason.

The public use of one’s reason must always be free, and it alone can bring about enlightenment among men.