| | Religion is too important a matter to its devotees to be a subject of ridicule. If they indulge in absurdities, they are to be pitied rather than ridiculed. |
| | We are not rich because of the things that we possess, but for what we can do without possessing them. |
| | Only the descent into the hell of self-knowledge can pave the way to godliness. |
| | I ought never to act except in such a way that I could also will that my maxim should become a universal law. |
| | Morality is not properly the doctrine of how we may make ourselves happy, but how we may make ourselves worthy of happiness. |
| | All our knowledge begins with the senses, proceeds then to the understanding, and ends with reason. There is nothing higher than reason. |
| | All thought must, directly or indirectly, by way of certain characters, relate ultimately to intuitions, and therefore, with us, to sensibility, because in no other way can an object be given to us. |
| | Always recognize that human individuals are ends, and do not use them as means to your end. |
| | Apart from moral conduct, all that man thinks himself able to do in order to become acceptable to God is mere superstition and religious folly. |
| | Beneficence is a duty. He who frequently practices it, and sees his benevolent intentions realized, at length comes really to love him to whom he has done good. When, therefore, it is said, "Thou shalt love thy neighbor as thyself," it is not meant, thou shalt love him first and do him good in consequence of that love, but thou shalt do good, to thy neighbor; and this thy beneficence will engender in thee that love to mankind which is the fulness and consummation of the inclination to do, good. |
| | By a lie a man throws away and, as it were, annihilates his dignity as a man. |
| | Do what is right, though the world may perish. |
| | Even philosophers will praise war as ennobling mankind, forgetting the Greek who said: War is bad in that it begets more evil than it kills. |
| | Experience without theory is blind, but theory without experience is mere intellectual play. |
| | Fallacious and misleading arguments are most easily detected if set out in correct syllogistic form. |
| | Happiness is not an ideal of reason, but of imagination. |
| | Have patience awhile; slanders are not long-lived. Truth is the child of time; erelong she shall appear to vindicate thee. |
| | He who has made great moral progress ceases to pray. |
| | If man makes himself a worm he must not complain when he is trodden on. |
| | If we attend to the course of conversation in mixed companies consisting not merely of scholars and subtle reasoners but also of business people or women, we notice that besides storytelling and jesting they have another entertainment, namely, arguing. |
| | Immaturity is the incapacity to use one's intelligence without the guidance of another. |
| | In law a man is guilty when he violates the rights of others. In ethics he is guilty if he only thinks of doing so. |
| | Intuition and concepts constitute... the elements of all our knowledge, so that neither concepts without an intuition in some way corresponding to them, nor intuition without concepts, can yield knowledge. |
| | It is not God's will merely that we should be happy, but that we should make ourselves happy. |
| | It is not necessary that whilst I live I live happily; but it is necessary that so long as I live I should live honourably. |
| | Man must be disciplined, for he is by nature raw and wild. |
| | Metaphysics is a dark ocean without shores or lighthouse, strewn with many a philosophic wreck. |
| | Morality is not really the doctrine of how to make ourselves happy but of how we are to be worthy of happiness. |
| | Nothing is divine but what is agreeable to reason. |
| | Out of the crooked timber of humanity, no straight thing was ever made. |
| | From such crooked wood as that which man is made of, nothing straight can be fashioned. |
| | Reason can never prove the existence of God. |
| | Reason does not work instinctively, but requires trial, practice, and instruction in order to gradually progress from one level of insight to another. |
| | Reason must approach nature in order to be taught by it. It must not, however, do so in the character of a pupil who listens to everything that the teacher chooses to say, but of an appointed judge who compels the witness to answer questions which he has himself formulated. |
| | Science is organized knowledge. Wisdom is organized life. |
| | Seek not the favor of the multitude; it is seldom got by honest and lawful means. But seek the testimony of few; and number not voices, but weigh them. |
| | The death of dogma is the birth of morality. |
| | The eternal mystery of the world is its comprehensibility. |
| | The history of the human race, viewed as a whole may be regarded as the realization of a hidden plan of nature to bring about a political constitution, internally, and for this purpose, also externally perfect, as the only state in which all the capacities implanted by her in mankind can be fully developed. |
| | The only objects of practical reason are therefore those of good and evil. For by the former is meant an object necessarily desired according to a principle of reason; by the latter one necessarily shunned, also according to a principle of reason. |
| | The possession of power unavoidably spoils the free use of reason. |
| | To be is to do. |