I have in this treatise followed the mathematical method, if not with all strictness, at least imitatively, not in order, by a display of profundity, to procure a better reception for it, but because I believe such a system to be quite capable of it, and that perfection may in time be obtained by a cleverer hand, if stimulated by this sketch, mathematical investigators of nature should find it not unimportant to treat the metaphysical portion, which anyway cannot be got rid of, as a special fundamental department of general physics, and to bring it into unison with the mathematical doctrine of motion.

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

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

All our knowledge falls with the bounds of experience.

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.

A plant, an animal, the regular order of nature — probably also the disposition of the whole universe — give manifest evidence that they are possible only by means of and according to ideas; that, indeed, no one creature, under the individual conditions of its existence, perfectly harmonizes with the idea of the most perfect of its kind — just as little as man with the idea of humanity, which nevertheless he bears in his soul as the archetypal standard of his actions; that, notwithstanding, these ideas are in the highest sense individually, unchangeably, and completely determined, and are the original causes of things; and that the totality of connected objects in the universe is alone fully adequate to that idea.

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

Human reason is by nature architectonic.

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.

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

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.

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.

Newton... (after having remarked that geometry only requires two of the mechanical actions which it postulates, namely, to describe a straight line and a circle) says: geometry is proud of being able to achieve so much while taking so little from extraneous sources. One might say of metaphysics, on the other hand: it stands astonished, that with so much offered it by pure mathematics it can effect so little. In the meantime, this little is something which mathematics indispensably requires in its application to natural science, which, inasmuch as it must here necessarily borrow from metaphysics, need not be ashamed to allow itself to be seen in company with the latter.

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.

Mathematics, from the earliest times to which the history of human reason can reach, has followed, among that wonderful people of the Greeks, the safe way of science. But it must not be supposed that it was as easy for mathematics as for logic, in which reason is concerned with itself alone, to find, or rather to make for itself that royal road. I believe, on the contrary, that there was a long period of tentative work (chiefly still among the Egyptians), and that the change is to be ascribed to a revolution, produced by the happy thought of a single man, whose experiments pointed unmistakably to the path that had to be followed, and opened and traced out for the most distant times the safe way of a science. The history of that intellectual revolution, which was far more important than the passage round the celebrated Cape of Good Hope, and the name of its fortunate author, have not been preserved to us. ... A new light flashed on the first man who demonstrated the properties of the isosceles triangle (whether his name was Thales or any other name), for he found that he had not to investigate what he saw hi the figure, or the mere concepts of that figure, and thus to learn its properties; but that he had to produce (by construction) what he had himself, according to concepts a priori, placed into that figure and represented in it, so that, in order to know anything with certainty a priori, he must not attribute to that figure anything beyond what necessarily follows from what he has himself placed into it, in accordance with the concept.

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.

When Galilei let balls of a particular weight, which he had determined himself, roll down an inclined plain, or Torricelli made the air carry a weight, which he had previously determined to be equal to that of a definite volume of water; or when, in later times, Stahl changed metal into lime, and lime again into metals, by withdrawing and restoring something, a new light flashed on all students of nature. They comprehended that reason has insight into that only, which she herself produces on her own plan, and that she must move forward with the principles of her judgments, according to fixed law, and compel nature to answer her questions, but not let herself be led by nature, as it were in leading strings, because otherwise accidental observations made on no previously fixed plan, will never converge towards a necessary law, which is the only thing that reason seeks and requires. Reason, holding in one hand its principles, according to which concordant phenomena alone can be admitted as laws of nature, and in the other hand the experiment, which it has devised according to those principles, must approach nature, in order to be taught by it: but not in the character of a pupil, who agrees to everything the master likes, but as an appointed judge, who compels the witnesses to answer the questions which he himself proposes. Therefore even the science of physics entirely owes the beneficial revolution in its character to the happy thought, that we ought to seek in nature (and not import into it by means of fiction) whatever reason must learn from nature, and could not know by itself, and that we must do this in accordance with what reason itself has originally placed into nature. Thus only has the study of nature entered on the secure method of a science, after having for many centuries done nothing but grope in the dark.

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

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.

That all our knowledge begins with experience there can be no doubt. For how is it possible that the faculty of cognition should be awakened into exercise otherwise than by means of objects which affect our senses, and partly of them selves produce representations, partly rouse our powers of understanding into activity, to compare, to connect, or to separate these, and so to convert the raw material of our sensuous impressions into a knowledge of objects, which is called experience? In respect of time, therefore, no knowledge of ours is antecedent to experience, but begins with it. But though all our knowledge begins with experience, it by no means follows, that all arises out of experience. For, on the contrary, it is quite possible that our empirical knowledge is a compound of that which we receive through impressions, and that which the faculty of cognition supplies from itself (sensuous impressions giving merely the occasion)... It is, therefore, a question which requires close investigation, and is not to be answered at first sight,—whether there exists a knowledge altogether independent of experience, and even of all sensuous impressions? Knowledge of this kind is called à priori, in contradistinction to empirical knowledge which has its sources à posteriori, that is, in experience.

The light dove, cleaving the air in her free flight, and feeling its resistance, might imagine that its flight would be still easier in empty space.

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

It is precisely in knowing its limits that philosophy consists.

He [Jesus] combines all duties (1) in one universal rule (which includes within itself both the inner and the outer moral relations of men), namely: Perform your duty for no motive other than unconditioned esteem for duty itself, i.e., love God (the Legislator of all duties) above all else; and (2) in a particular rule, that, namely, which concerns man’s external relation to other men as universal duty: Love every one as yourself, i.e., further his welfare from good-will that is immediate and not derived from motives of self-advantage. These commands are not mere laws of virtue but precepts of holiness which we ought to pursue, and the very pursuit of them is called virtue. Accordingly he destroys the hope of all who intend to wait upon this moral goodness quite passively, with their hands in their laps, as though it were a heavenly gift which descends from on high. He who leaves unused the natural predisposition to goodness which lies in human nature (like a talent entrusted to him) in lazy confidence that a higher moral influence will no doubt supply the moral character and completeness which he lacks, is confronted with the threat that even the good which, by virtue of his natural predisposition, he may have done, will not be allowed to stand him in stead because of this neglect (XXV, 29).

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.”

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.

Von einem tungusischen Schaman, bis zu dem Kirche und Staat zugleich regierenden europäischen Prälaten … ist zwar ein mächtiger Abstand in der Manier, aber nicht im Prinzip, zu glauben; denn was dieses betrifft, so gehören sie insgesammt zu einer und derselben Klasse, derer nämlich, die in dem, was an sich keinen bessern Menschen ausmacht (im Glauben gewisser statutarischer Sätze, oder Begehen gewisser willkürlicher Observanzen), ihren Gottesdienst setzen. Diejenigen allein, die ihn lediglich in der Gesinnung eines guten Lebenswandels zu finden gemeint sind, unterscheiden sich von jenen durch den Ueberschritt zu einem ganz andern und über das erste weit erhabenen Prinzip.

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. p. 251

Although individuals who have begun to awake to freedom of cogitation, after having long unconsciously slumbered under the yoke of a belief (e.g. Protestants), do straightway deem themselves ennobled, in proportion to their articles of belief are scanty; yet, singularly enough, they whose understandings still lie dormant, cling to a very different principle of safety. “Better Believe Too Much Than Believe Too Little,” is here the adage; for whatever is done beyond and above what is duty, cannot in any event harm, but may perchance to good. Upon this delusive dream, which would make dishonesty the very spirit and soul of religious confession, is based on the well-known argumentum a tuto, which obtains a more easy and extended currency, because religion compensates for every fault, and hence also for dishonesty in adopting it. If, says the [https://en.wiktionary.org/wiki/sciolist sciolist], what I profess to believe concerning the Godhead is correct, then I have precisely hit the very truth. Should, on the other hand, the articles contain an error, still, as there is nothing in them morally improper, then have I merely assented to something superfluous and unnecessary, by all which I have no doubt molested, but certainly not incriminated myself. The peril arising out of the improbity of his profession – The Lesson of Conscience-necessarily undergone, when what is declared in the presence of God to be certain, which mankind must nevertheless know not to be so constituted as to admit of being affirmed with unconditioned certainty, are all overlooked by this dishonest maxim, And Indeed Pass With The Hypocrite For Nothing. The genuine safety-principle of true religion is contrariwise as follows. Whatever is a mean or condition of future bliss, unknown to naked reason, and promulgated singly by revelation, can strike root in my conviction, just like any other history; and so far forth as it does not militate against morality, cannot be absolutely false. Besides leaving this point totally undecided, I may unquestionably trust, that whatever of salutary there may lie in a document, will stand me in good stead, provided I do not by my moral short-coming make myself unworthy of it. In this maxim, there is a real moral safety, viz. That conscience be not violated; and more cannot be demanded from mankind. There is, moreover, an utmost danger and insecurity in that lauded stratagem of expediency, whereby we think astutely to evade any disadvantageous sequents that may spring from unbelieving nonconformity. Thus tampering with either party, we destroy our credit with both.

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.

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.

Human freedom is realised in the adoption of humanity as an end in itself, for the one thing that no-one can be compelled to do by another is to adopt a particular end.

He [Jesus] claims that not the observance of outer civil or statutory churchly duties but the pure moral disposition of the heart alone can make man well-pleasing to God (Matthew V, 20-48); … that injury done one’s neighbor can be repaired only through satisfaction rendered to the neighbor himself, not through acts of divine worship (V, 24). Thus, he says, does he intend to do full justice to the Jewish law (V, 17); whence it is obvious that not scriptural scholarship but the pure religion of reason must be the law’s interpreter, for taken according to the letter, it allowed the very opposite of all this. Furthermore, he does not leave unnoticed, in his designations of the strait gate and the narrow way, the misconstruction of the law which men allow themselves in order to evade their true moral duty, holding themselves immune through having fulfilled their churchly duty (VII, 13). He further requires of these pure dispositions that they manifest themselves also in works (VII, 16) and, on the other hand, denies the insidious hope of those who imagine that, through invocation and praise of the Supreme Lawgiver in the person of His envoy, they will make up for their lack of good works and ingratiate themselves into favor (VII, 21). Regarding these works he declares that they ought to be performed publicly, as an example for imitation (V, 16), and in a cheerful mood, not as actions extorted from slaves (VI, 16); and that thus, from a small beginning in the sharing and spreading of such dispositions, religion, like a grain of seed in good soil, or a ferment of goodness, would gradually, through its inner power, grow into a kingdom of God (XIII, 31-33).

Let us suppose there was a teacher of whom an historical record (or, at least, a widespread belief which is not basically disputable) reports that he was the first to expound publicly a pure and searching religion, comprehensible to the whole world. … Suppose that all he did was done even in the face of a dominant ecclesiastical faith which was onerous and not conducive to moral ends (a faith whose perfunctory worship can serve as a type of all the other faiths, at bottom merely statutory, which were current in the world at the time). Suppose, further, we find that he had made this universal religion of reason the highest and indispensable condition of every religious faith whatsoever … and this without further adding to this faith burdensome new ordinances or wishing to transform acts which he had initiated into peculiar holy practices, required in themselves as being constituent elements of religion. After this description one will not fail to recognize the person who can be referenced, not indeed as the founder of the religion which, free from every dogma, is engraved in all men’s hearts (for it does not have its origin in an arbitrary will), but as the founder of the first true church.

For it is extremely absurd to expect to be enlightened by reason, and yet to prescribe to her beforehand on which side she must incline.

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?

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.

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.

Two things fill the mind with ever new and increasing admiration and awe, the oftener and the more steadily we reflect on them: the starry heavens above and the moral law within. I have not to search for them and conjecture them as though they were veiled in darkness or were in the transcendent region beyond my horizon; I see them before me and connect them directly with the consciousness of my existence. The former begins from the place I occupy in the external world of sense, and enlarges my connection therein to an unbounded extent with worlds upon worlds and systems of systems, and moreover into limitless times of their periodic motion, its beginning and continuance. The second begins from my invisible self, my personality, and exhibits me in a world which has true infinity, but which is traceable only by the understanding, and with which I discern that I am not in a merely contingent but in a universal and necessary connection, as I am also thereby with all those visible worlds. The former view of a countless multitude of worlds annihilates as it were my importance as an animal creature, which after it has been for a short time provided with vital power, one knows not how, must again give back the matter of which it was formed to the planet it inhabits (a mere speck in the universe). The second, on the contrary, infinitely elevates my worth as an intelligence by my personality, in which the moral law reveals to me a life independent of animality and even of the whole sensible world, at least so far as may be inferred from the destination assigned to my existence by this law, a destination not restricted to conditions and limits of this life, but reaching into the infinite.

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

it is absurd … to hope that maybe another Newton may some day arise, to make intelligible to us even the genesis of but a blade of grass ("Dialectic of Teleological Judgment" §75)

That religion in which I must know in advance that something is a divine command in order to recognize it as my duty, is the revealed religion (or the one standing in need of a revelation); in contrast, that religion in which I must first know that something is my duty before I can accept it as a divine injunction is the natural religion. … When religion is classified not with reference to its first origin and its inner possibility (here it is divided into natural and revealed religion) but with respect to its characteristics which make it capable of being shared widely with others, it can be of two kinds: either the natural religion, of which (once it has arisen) everyone can be convinced through his own reason, or a learned religion, of which one can convince others only through the agency of learning (in and through which they must be guided). … A religion, accordingly, can be natural, and at the same time revealed, when it is so constituted that men could and ought to have discovered it of themselves merely through the use of their reason, although they would not have come upon it so early, or over so wide an area, as is required. Hence a revelation thereof at a given time and in a given place might well be wise and very advantageous to the human race, in that, when once the religion thus introduced is here, and has been made known publicly, everyone can henceforth by himself and with his own reason convince himself of its truth. In this event the religion is objectively a natural religion, though subjectively one that has been revealed.

There is needed, no doubt, a body of servants (ministerium) of the invisible church, but not officials (officiales), in other words, teachers but not dignitaries, because in the rational religion of every individual there does not yet exist a church as a universal union (omnitudo collectiva).

Only the descent into the hell of self-knowledge can pave the way to godliness.

If it were right to overstep a little the limits of apodictic certainty befitting metaphysics, it would seem worth while to trace out some things pertaining not merely to the laws but even to the causes of sensuous intuition, which are only intellectually knowable. Of course the human mind is not affected by external things, and the world does not lie open to its insight infinitely, except as far as itself together with all other things is sustained by the same infinite power of one. Hence it does not perceive external things but by the presence of the same common sustaining cause; and hence space, which is the universal and necessary condition of the joint presence of everything known sensuously, may be called the phenomenal omnipresence, for the cause of the universe is not present to all things and everything, as being in their places, but their places, that is the relations of the substances, are possible, because it is intimately present to all. Furthermore, since the possibility of the changes and successions of all things whose principle as far as sensuously known resides in the concept of time, supposes the continuous existence of the subject whose opposite states succeed; that whose states are in flux, lasting not, however, unless sustained by another; the concept of time as one infinite and immutable in which all things are and last, is the phenomenal eternity of the general cause} But it seems more cautious to hug the shore of the cognitions granted to us by the mediocrity of our intellect than to be carried out upon the high seas of such mystic investigations, like Malebranche, whose opinion that we see all things in God is pretty nearly what has here been expounded.

The guardians who have kindly undertaken the supervision will see to it that by far the largest part of mankind, including the entire "beautiful sex," should consider the step into maturity, not only as difficult but as very dangerous. After having made their domestic animals dumb and having carefully prevented these quiet creatures from daring to take any step beyond the lead-strings to which they have fastened them, these guardians then show them the danger which threatens them, should they attempt to walk alone.

It is difficult for the isolated individual to work himself out of the immaturity which has become almost natural for him. He has even become fond of it and for the time being is incapable of employing his own intelligence, because he has never been allowed to make the attempt. Statutes and formulas, these mechanical tools of a serviceable use, or rather misuse, of his natural faculties, are the ankle-chains of a continuous immaturity. Whoever threw it off would make an uncertain jump over the smallest trench because he is not accustomed to such free movement. Therefore there are only a few who have pursued a firm path and have succeeded in escaping from immaturity by their own cultivation of the mind.

There will always be some people who think for themselves, even among the self-appointed guardians of the great mass who, after having thrown off the yoke of immaturity themselves, will spread about them the spirit of a reasonable estimate of their own value and of the need for every man to think for himself.

A public can only arrive at enlightenment slowly. Through revolution, the abandonment of personal despotism may be engendered and the end of profit-seeking and domineering oppression may occur, but never a true reform of the state of mind. Instead, new prejudices, just like the old ones, will serve as the guiding reins of the great, unthinking mass. All that is required for this enlightenment is freedom; and particularly the least harmful of all that may be called freedom, namely, the freedom for man to make public use of his reason in all matters. But I hear people clamor on all sides: Don't argue! The officer says: Don't argue, drill! The tax collector: Don't argue, pay! The pastor: Don't argue, believe!

The public use of a man's reason must be free at all times, and this alone can bring enlightenment among men...