“In every department of physical science there is only so much science, properly so-called, as there is mathematics.”

“All rational knowledge is either material, and concerns some objects, or formal, and is occupied only with the form of understanding and reason itself and with the universal rules of thinking, without regard to distinctions among objects. formal philosophy is called logic. Material philosophy, however, which has to do with definite object objects and the laws to which they are subject, is divided into two parts. This is because these laws are either laws of nature or laws of freedom. The science of the former is called physics, and that of the latter ethics. The former is also called theory of nature and the latter theory of morals.”

“...new prejudices will serve as well as old ones to harness the great unthinking masses.For this enlightenment, however, nothing is required but freedom, and indeed the most harmless among all the things to which this term can properly be applied. It is the freedom to make public use of one's reason at every point. But I hear on all sides, 'Do not argue!' The Officer says: 'Do not argue but drill!' The tax collector: 'Do not argue but pay!' The cleric: 'Do not argue but believe!' Only one prince in the world says, 'Argue as much as you will, and about what you will, but obey!' Everywhere there is restriction on freedom.”

“Laziness and cowardice are the reasons why so great a portion of mankind, after nature has long since discharged them from external direction (naturaliter maiorennes), nevertheless remains under lifelong tutelage, and why it is so easy for others to set themselves up as their guardians. It is so easy not to be of age. If I have a book which understands for me, a pastor who has a conscience for me, a physician who decides my diet, and so forth, I need not trouble myself. I need not think, if I can only pay - others will easily undertake the irksome work for me.That the step to competence is held to be very dangerous by the far greater portion of mankind...”

“Faulheit und Feigheit sind die Ursachen, warum ein so großer Teil der Menschen, nachdem sie die Natur längst von fremder Leitung frei gesprochen, dennoch gerne zeitlebens unmündig bleiben; und warum es anderen so leicht wird, sich zu deren Vormündern aufzuwerfen.”

“Handle so, daß die Maxime deines Willens jederzeit zugleich als Prinzip einer allgemeinen Gesetzgebung gelten könne.”

“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.”