The more we devote ourselves to observing animals and their behaviour, the more we love them, on seeing how gready they care for their young; in such a context, we cannot even contemplate cruelty to a wolf. Leibnitz put the grub he had been observing back on the tree with its leaf, lest he should be guilty of doing any harm to it. It upsets a man to destroy such a creature for no reason, and this tenderness is subsequently transferred to man.

Metaphysics has as the proper object of its enquiries three ideas only: God, freedom, and immortality.

All... good and useful properties of character have a price in exchange for others which have just as much use. Talent has a market price, since the sovereign or estate-owner can use a talented person in all sorts of ways. Temperament has a fancy price,22 since one can converse well with such a person; he is a pleasant companion. But, character has an inner value[,] and it is above all price.

When the man governed by self-interest, the god of this world, does not renounce it but merely refines it by the use of reason and extends it beyond the constricting boundary of the present, he is represented (Luke XVI, 3-9) as one who, in his very person [as servant], defrauds his master [self- interest] and wins from him sacrifices in behalf of "duty."

I am an investigator by inclination. I feel a great thirst for knowledge and an impatient eagerness to advance, also satisfaction at each progressive step. There was a time when I thought that all this could constitute the honor of humanity, and I despised the mob, which knows nothing about it. Rousseau set me straight. This dazzling excellence vanishes; I learn to honor men, and would consider myself much less useful than common laborers if I did not believe that this consideration could give all the others a value, to establish the rights of humanity.

Thoughts without content are empty, intuitions without concepts are blind. The understanding can intuit nothing, the senses can think nothing. Only through their unison can knowledge arise.

Through failures one becomes intelligent; but the one who has trained himself in this subject so that he can make others wise through their own failures, has used his intelligence. Ignorance is not stupidity.

All the interests of my reason, speculative as well as practical, combine in the three following questions: 1. What can I know? 2. What ought I to do? 3. What may I hope?

Good and strong will. Mechanism must precede science (learning). Also in morals and religion? Too much discipline makes one narrow and kills proficiency. Politeness belongs, not to discipline, but to polish, and thus comes last.

Human reason has this peculiar fate that in one species of its knowledge it is burdened by questions which, as prescribed by the very nature of reason itself, it is not able to ignore, but which, as transcending all its powers, it is also not able to answer.

Habit... makes the endurance of evil easy (which, under the name of patience, is falsely honored as a virtue), because sensations of the same type, when continued without alteration for a long time, draw our attention away from the senses so that we are scarcely conscious of them at all. On the other hand, habit also makes the consciousness and the remembrance of good that has been received more difficult, which then gradually leads to ingratitude (a real vice). [...] Acquired habit deprives good actions of their moral value because it undermines mental freedom and, moreover, it leads to thoughtless repetitions of the same acts (monotony), and thus becomes ridiculous.

Thus our duties to animals are indirectly duties to humanity.

Human reason is by nature architectonic.

Nature made women mature early and had them demand gentle and polite treatment from men, so that they would find themselves imperceptibly fettered by a child due to their own magnanimity; and they would find themselves brought, if not quite to morality itself, then at least to that which cloaks it, moral behavior, which is the preparation and introduction to morality.

Christianity possesses the great advantage over Judaism of being represented as coming from the mouth of the first Teacher not as a statutory but as a moral religion, and as thus entering into the closest relation with reason so that, through reason, it was able of itself, without historical learning, to be spread at all times and among all peoples with the greatest trustworthiness.

In the metaphysical elements of aesthetics the various nonmoral feelings are to be made use of; in the elements of moral metaphysics the various moral feelings of men, according to the differences in sex, age, education, and government, of races and climates, are to be employed.

Psychologists have hitherto failed to realize that imagination is a necessary ingredient of perception itself.

The deceiver is really the fool.

The inscrutable wisdom through which we exist is not less worthy of veneration in respect to what it denies us than in respect to what it has granted.

There must be a seed of every good thing in the character of men, otherwise no one can bring it out. Lacking that, analogous motives, honor, etc., are substituted. Parents are in the habit of looking out for the inclinations, for the talents and dexterity, perhaps for the disposition of their children, and not at all for their heart or character.

Abbot Terrasson tells us that if the size of a book were measured not by the number of its pages but by the time required to understand it, then we could say about many books that they would be much shorter were they not so short.

Collectively, the more civilized men are, the more they are actors. They assume the appearance of attachment, of esteem for others, of modesty, and of disinterestedness, without ever deceiving anyone, because everyone understands that nothing sincere is meant. Persons are familiar with this, and it is even a good thing that this is so in this world, for when men play these roles, virtues are gradually established, whose appearance had up until now only been affected. These virtues ultimately will become part of the actor's disposition. To deceive the deceiver in ourselves, or the tendency to deceive, is a fresh return to obedience.

This proof can at most, therefore, demonstrate the existence of an architect of the world, whose efforts are limited by the capabilities of the material with which he works, but not of a creator of the world, to whom all things are subject.

The woman wants to dominate, the man wants to be dominated.

All natural philosophers, who wished to proceed mathematically in their work, have hence invariably (although unknown to themselves) made use of metaphysical principles, and must make use of such, it matters not how energetically they may otherwise repudiate any claim of metaphysics on their science.

The question here is not, "How conscience ought to be guided? For Conscience is its own General and Leader; it is therefore enough that each man have one. What we want to know is, how conscience can be her own Ariadne, and disentangle herself from the mazes even of the most raveled and complicated casuistical theology. Here is an ethical proposition that stands in need of no proof: No Action May At Any Time Be Hazarded On The Uncertainty That Perchance It May Not Be Wrong (Quod dubitas, ne feceris! Pliny - which you doubt, then neither do) Hence the Consciousness, that Any Action I am about to perform is Right, is in itself a most immediate and imperative duty. What actions are right, - what wrong - is a matter for the understanding, not for conscience.

In the natural state no concept of God can arise, and the false one which one makes for himself is harmful. Hence the theory of natural religion can be true only where there is no science; therefore it cannot bind all men together.

I have no knowledge of myself as I am, but merely as I appear to myself.

What alone has value is the use to which life is put and the end to which it is directed. The value of life has to be created by man, it cannot be obtained through luck but only through wisdom. He who is anxiously concerned over losing his life will never enjoy life.

Two things fill the mind with ever-increasing wonder and awe, the more often and the more intensely the mind of thought is drawn to them: the starry heavens above me and the moral law within me.

Character means that the person derives his rules of conduct from himself and from the dignity of humanity. Character is the common ruling principle in man in the use of his talents and attributes. Thus it is the nature of his will, and is good or bad. A man who acts without settled principles, with no uniformity, has no character. A man may have a good heart and yet no character, because he is dependent upon impulses and does not act according to maxims. Firmness and unity of principle are essential to character.

I have therefore found it necessary to deny knowledge in order to make room for faith.

Young man! Deny yourself satisfaction (of amusement, of debauchery, of love, etc.), not with the Stoical intention of complete abstinence, but with the refined Epicurean intention of having in view an ever-growing pleasure. This stinginess with the cash of your vital urge makes you definitely richer through the postponement of pleasure, even if you should, for the most part, renounce the indulgence of it until the end of your life. The awareness of having pleasure under your control is, like everything idealistic, more fruitful and more abundant than everything that satisfies the sense through indulgence because it is thereby simultaneously consumed and consequently lost from the aggregate of totality.

All human knowledge begins with intuitions, proceeds from thence to concepts, and ends with ideas.

England and France, the two most civilized nations on earth, who are in contrast to each other because of their different characters, are, perhaps chiefly for that reason, in constant feud with one another. Also, England and France, because of their inborn characters, of which the acquired and artificial character is only the result, are probably the only nations who can be assumed to have a particular and, as long as both national characters are not blended by the force of war, unalterable characteristics. That French has become the universal language of conversation, especially in the feminine world, and that English is the most widely used language of commerce among tradesmen, probably reflects the difference in their continental and insular geographic situation.

All true metaphysics is taken from the essential nature of the thinking faculty itself, and therefore in nowise invented, since it is not borrowed from experience, but contains the pure operations of thought, that is, conceptions and principles à priori, which the manifold of empirical presentations first of all brings into legitimate connection, by which it can become empirical knowledge, i.e. experience. ...mathematical physicists were thus quite unable to dispense with such metaphysical principles...

The universal and lasting establishment of peace constitutes not merely a part, but the whole final purpose and end of the science of right as viewed within the limits of reason.

Man has his own inclinations and a natural will which, in his actions, by means of his free choice, he follows and directs. There can be nothing more dreadful than that the actions of one man should be subject to the will of another; hence no abhorrence can be more natural than that which a man has for slavery. And it is for this reason that a child cries and becomes embittered when he must do what others wish, when no one has taken the trouble to make it agreeable to him. He wants to be a man soon, so that he can do as he himself likes.

All our knowledge falls with the bounds of experience.

Money is the password, and all doors, which are closed to the man of lesser means, fly open to those whom Plutus favors. The invention of money, which has no other usefulness (or at least it should not have any) except for the commercial exchange of the products of man's industry, now serves all that is physically good among men. Especially after money was represented by metal, it has produced avarice which, finally, without indulgence, but by its mere possession, and even with the resolution (of the stingy) not to spend it, still contains a power which people believe can sufficiently compensate for the lack of any other power.

Morality is not properly the doctrine of how we may make ourselves happy, but how we may make ourselves worthy of happiness.

The more one presupposes that his own power will suffice him to realize what he desires the more practical is that desire. When I treat a man contemptuously, I can inspire him with no practical desire to appreciate my grounds of truth. When I treat any one as worthless, I can inspire him with no desire to do right.

Criticism alone can sever the root of materialism, fatalism, atheism, free-thinking, fanaticism, and superstition, which can be injurious universally; as well as of idealism and skepticism, which are dangerous chiefly to the Schools, and hardly allow of being handed on to the public.

To require that a so-called layman should not use his own reason in religious matters, particularly since religion is to be appreciated as moral, but instead follow the appointed clergyman and thus someone else's reason, is an unjust demand because as to morals every man must account for all his doings. The clergyman will not and even cannot assume such a responsibility.

Philosophical knowledge is the knowledge gained by reason from concepts; mathematical knowledge is the knowledge gained by reason from the construction of concepts.

The first characteristic of the human species is man's ability, as a rational being, to establish character for himself, as well as for the society into which nature has placed him. This ability, however, presupposes an already favorable natural predisposition and an inclination to the good in man, because the evil is really without character (since it is at odds with itself, and since it does not tolerate any lasting principle within itself)

Natural science is throughout either a pure or an applied doctrine of motion.

Even if a civil society were to be dissolved by the consent of all its members (e.g., if a people inhabiting an island decided to separate and disperse throughout the world), the last murderer remaining in prison would first have to be executed, so that each has done to him what his deeds deserve and blood guilt does not cling to the people for not having insisted upon this punishment; for otherwise the people can be regarded as collaborators in his public violation of justice.

Suicide evokes revulsion with horror, because everything in nature seeks to preserve itself: a damaged tree, a living body, an animal; and in man, then, is freedom, which is the highest degree of life, and constitutes the worth of it, to become now a principium for self-destruction? This is the most horrifying thing imaginable. For anyone who has already got so far as to be master, at any time, over his own life, is also master over the life of anyone else; for him, the door stands open to every crime, and before he can be seized he is ready to spirit himself away out of the world. So suicide evokes horror, in that a man thereby puts himself below the beasts. We regard a suicide as a carcase, whereas we feel pity for one who meets his end through fate.

It is therefore correct to say that the senses do not err - not because they always judge rightly, but because they do not judge at all.