Klagenfurt, in the beginning of the year 1794

Honored and sincerely beloved man,

Please don't take offense and do grant me, with your customary good will, the pleasure of writing to you again. For when I write to you I feel the highest pleasure: the feeling of awe and of love for your person – you who ennoble humanity. And I need not prove to you that this is the feeling that makes us blessed, because you had the good fortune to locate for us this purest and most sacred of feelings and to rescue it forever from religious institutions. I must thank you most warmly for “Religion within the Bounds of Reason,” thank you in the name of all who have managed to tear themselves loose from those ensnaring chains of darkness. Do not deprive us of your wise guidance so long as you think that there is still something we lack, for it is not our desire or our satisfaction that can judge what we need but only your perception of us. I felt myself wholly informed by the Critique of Pure Reason, and yet I found that your subsequent works were not in the least superfluous. Gladly would I have commanded the course of nature to stand still if that could assure me that you would have the time you need to complete what you have begun for us, and gladly would I attach the days of my future life to your own if I could thereby know that you were still alive when the end of the French Revolution comes about.

I hope that a copy of the second edition of my Critique will have been conveyed to you, dear friend, by Herr Grunert of Halle; if not, the enclosed letter to him, which I beg you to post, should take care of it.

If you think it necessary to arrange for a review of this second edition, I would be very grateful if it took note of an error in transcription that troubles me. Something like this:

“In the Preface, p. xi, the third line from the bottom contains a copying error, since “equilateral” is written instead of “equiangular” triangle. (Euclid's Elements, Bk. I, Prop. 5.)”

For even though in Diogenes Laertes' version one can easily see that the latter is intended, not every reader has a copy of Diogenes readily available.

My publisher commissioned a Latin translation of the second edition of my Critique, by Professor Born in Leipzig. You were kind enough to offer to inspect his completed translation if it is sent to you a section at a time, to make sure that the style, which might aim too much at elegance, be more or less Scholastic if not quite Old Latin in its precision and correctness. If your kind offer is still valid, please let me know what my publisher will owe you for your trouble. From me you will have the greatest gratitude. I have sought to inform Prof. Born of this plan in my enclosed letter.

Noble Sir,

Honored Herr Professor,

I am taking advantage of the opportunity I have of sending you my [Inaugural] Dissertation by way of the respondent of that work, a capable Jewish student of mine. At the same time, I should like to destroy an unpleasant misunderstanding caused by my protracted delay in answering your valued letter. The reason was none other than the striking importance of what I gleaned from that letter, and this occasioned the long postponement of a suitable answer. Since I had spent much time investigating the science on which you focused your attention there, for I was attempting to discover the nature and if possible the manifest and immutable laws of that science, it could not have pleased me more that a man of such discriminating acuteness and universality of insight, with whose method of thinking I had often been in agreement, should offer his services for a joint project of tests and investigations, to map the secure construction of this science. I could not persuade myself to send you anything less than a clear summary of how I view this science and a definite idea of the proper method for it. The carrying out of this intention entangled me in investigations that were new to me and, what with my exhausting academic work, necessitated one postponement after another.

Dear Herr Doctor,

Dearest friend,

Today Herr Mendelssohn, your worthy friend and mine (for so I flatter myself), is departing. To have a man like him in Königsberg on a permanent basis, as an intimate acquaintance, a man of such gentle temperament, good spirits, and enlightenment – how that would give my soul the nourishment it has lacked so completely here, a nourishment I miss more and more as I grow older! For as far as bodily nourishment goes, you know I hardly worry about that and I am quite content with my share of earthly goods. I fear I did not manage to take full advantage of my one opportunity to enjoy this rare man, partly because I worried about interfering with his business here. The day before yesterday he honored me by attending two of my lectures, taking potluck, so to speak, since the table was not set for such a distinguished guest. The lecture must have seemed somewhat incoherent to him, since I had to spend most of the hour reviewing what I had said before vacation. The clarity and order of the original lecture were largely absent. Please help me to keep up my friendship with this fine man.

You have made me two presents, dear friend, that show me that both in talent and in feeling you are that rare student who makes all the effort that goes into my often thankless job seem amply rewarded.

Esteemed Friend and Teacher,

I learn from you every week, so once again I submit my sincerest thanks for your excellent essay in the January issue of the Berlinische Monatschrift.

I beseech you now most respectfully for

1. the review of Dr. Hufeland's book, please send it soon,

2. a declaration stating whether Privy Councillor Jacobi has misunderstood you when, in his book on Spinoza, he introduces your ideas about space and says that they are “wholly in the spirit of Spinoza.”

It is truly incomprehensible how often you are misunderstood; there exist people who are really in other respects not imbeciles yet who take you to be an atheist.

I am sure that you too sincerely regret the unexpected death of the excellent Mendelssohn. But can that be why you hesitate to publish your work? You can tell how diligently the students here are studying your Critique of Pure Reason from the fact that, a few weeks ago, two students fought a duel because one of them had said to the other that he didn't understand your book and that it would take another thirty years of study before he would understand it and another thirty before he would be able to say anything about it.

If I should die before long, I think the only thing to which I could not easily reconcile myself would be to have missed seeing the completion of your labors. I await Easter with the most intense longing.

Finally my wish is fulfilled – my strongest wish ever since my heart and mind were brought into concord by that man who among all men of present and past ages is most significant to me, and who becomes and must become more significant to me with every progressive step my liberated spirit takes, he who is attached to my soul with a love as pure and indelible as is the light of cognition that he has kindled in me – in a word, my wish to be known and loved by you. And it is you to whom I shall owe not only the tranquillity and the most blessed employments but also the sweetest joy of my life, which I have been fortunate enough to find in having the respect and good favor of noble human beings.

My distinguished father-in-law takes joy in my joy. I conveyed your kind letter and the manuscript to him right away along with your flattering references to him. He asked me to write to you. He would be proud to think that his writings contributed to your entertainment. Your essay, an excellent adornment to his Merkur, was most welcome to him. For that reason he regrets that when the manuscript arrived the first sheet of the Merkur already had Jenner's work along with a historical essay by Schiller printed on it, so that the current new series had to be initiated with another name than yours.

Immanuel Kant's Critique of Pure Reason is one of the seminal and monumental works in the history of Western philosophy. Published in May 1781, when its author was already fifty-seven years old, and substantially revised for its second edition six years later, the book was both the culmination of three decades of its author's often very private work and the starting-point for nearly two more decades of his rapidly evolving but now very public philosophical thought. In the more than two centuries since the book was first published, it has been the constant object of scholarly interpretation and a continuous source of inspiration to inventive philosophers. To tell the whole story of the book's influence would be to write the history of philosophy since Kant, and that is beyond our intention here. After a summary of the Critique's structure and argument, this introduction will sketch its genesis and evolution from Kant's earliest metaphysical treatise in 1755 to the publication of the first edition of the Critique in 1781 and its revision for the second edition of 1787.

THE ARGUMENT OF THE CRITIQUE

The strategy of the Critique . In the conclusion to his second critique, the Critique of Practical Reason of 1788, Kant famously wrote, “Two things fill the mind with ever new and increasing admiration and awe the more often and more enduringly reflection is occupied with them: the starry heavens above me and the moral law within me.” This motto could just as well have served for virtually all of Kant's philosophical works, and certainly for the Critique of Pure Reason.

Section One The ideal in general.

We have seen above that no objects at all can be represented through pure concepts of the understanding without any conditions of sensibility, because the conditions for the objective reality of these concepts are lacking, and nothing is encountered in them except the pure form of thinking. Nevertheless they can be exhibited in concreto if one applies them to appearances; for in the latter they have the proper material for a concept of experience, which is nothing but a concept of the understanding in concreto. Ideas, however, are still more remote from objective reality than categories; for no appearance can be found in which they may be represented in concreto. They contain a certain completeness that no possible empirical cognition ever achieves, and with them reason has a systematic unity only in the sense that the empirically possible unity seeks to approach it without ever completely reaching it.

But something that seems to be even further removed from objective reality than the idea is what I call the ideal, by which I understand the idea not merely in concreto but in individuo, i.e., as an individual thing which is determinable, or even determined, through the idea alone.

In all subsumptions of an object under a concept the representations of the former must be homogeneous with the latter, i.e., the concept must contain that which is represented in the object that is to be subsumed under it, for that is just what is meant by the expression “an object is contained under a concept.” Thus the empirical concept of a plate has homogeneity with the pure geometrical concept of a circle, for the roundness that is thought in the former can be intuited in the latter.

Now pure concepts of the understanding, however, in comparison with empirical (indeed in general sensible) intuitions, are entirely un-homogeneous, and can never be encountered in any intuition. Now how is the subsumption of the latter under the former, thus the application of the category to appearances possible, since no one would say that the category, e.g., causality, could also be intuited through the senses and is contained in the appearance? This question, so natural and important, is really the cause which makes a transcendental doctrine of the power of judgment necessary, in order, namely, to show the possibility of applying pure concepts of the understanding to appearances in general. In all other sciences, where the concepts through which the object is thought in general are not so different and heterogeneous from those that represent it in concreto, as it is given, it is unnecessary to offer a special discussion of the application of the former to the latter.

The idea of transcendental philosophy.

Experience is without doubt the first product that our understanding brings forth as it works on the raw material of sensible sensations. It is for this very reason the first teaching, and in its progress it is so inexhaustible in new instruction that the chain of life in all future generations will never have any lack of new information that can be gathered on this terrain. Nevertheless it is far from the only field to which our understanding can be restricted. It tells us, to be sure, what is, but never that it must necessarily be thus and not otherwise. For that very reason it gives us no true universality, and reason, which is so desirous of this kind of cognitions, is more stimulated than satisfied by it. Now such universal cognitions, which at the same time have the character of inner necessity, must be clear and certain for themselves, independently of experience; hence one calls them a priori cognitions: whereas that which is merely borrowed from experience is, as it is put, cognized only a posteriori, or empirically.

Now what is especially remarkable is that even among our experiences cognitions are mixed in that must have their origin a priori and that perhaps serve only to establish connection among our representations of the senses.

This tide stands here only to designate a place that is left open in the system and must be filled in the future. I will content myself with casting a cursory glance from a merely transcendental point of view, namely that of the nature of pure reason, on the whole of its labors hitherto, which presents to my view edifices, to be sure, but only in ruins.

It is remarkable enough, although it could not naturally have been otherwise, that in the infancy of philosophy human beings began where we should now rather end, namely, by studying first the cognition of God and the hope or indeed even the constitution of another world. Whatever crude concepts of religion the old customs, which were left over from the rude state of the nations, may have introduced, these still did not prevent their more enlightened part from dedicating themselves to free investigations of this object, and it was readily understood that there could be no more fundamental and reliable way of pleasing the invisible power who rules the world, in order to be happy at least in another world, than the good conduct of life. Hence theology and morality were the two incentives, or better, the points of reference for all the abstract inquiries of reason to which we have always been devoted. The first, however, was really that which gradually drew purely speculative reason in its train, which subsequently became so famous under the name of metaphysics.

If I regard the sum total of all cognition of pure and speculative reason as an edifice for which we have in ourselves at least the idea, then I can say that in the Transcendental Doctrine of Elements we have made an estimate of the building materials and determined for what sort of edifice, with what height and strength, they would suffice. It turned out, of course, that although we had in mind a tower that would reach the heavens, the supply of materials sufficed only for a dwelling that was just roomy enough for our business on the plane of experience and high enough to survey it; however, that bold undertaking had to fail from lack, of material, not to mention the confusion of languages that unavoidably divided the workers over the plan and dispersed them throughout the world, leaving each to build on his own according to his own design. Now we are concerned not so much with the materials as with the plan, and, having been warned not to venture some arbitrary and blind project that might entirely exceed our entire capacity, yet not being able to abstain from the erection of a sturdy dwelling, we have to aim at an edifice in relation to the supplies given to us that is at the same time suited to our needs.

Reflection (reflexio) does not have to do with objects themselves, in order to acquire concepts directly from them, but is rather the state of mind in which we first prepare ourselves to find out the subjective conditions under which we can arrive at concepts.97 It is the consciousness of the relation d of given representations to our various sources of cognition, through which alone their relation among themselves can be correctly determined. The first question prior to all further treatment of our representation is this: In which cognitive faculty do they belong together? Is it the understanding or is it the senses before which they are connected or compared? Many a judgment is accepted out of habit, or connected through inclination: but since no reflection preceded or at least critically succeeded it, it counts as one that has received its origin in the understanding. Not all judgments require an investigation, i.e., attention to the grounds of truth; for if they are immediately certain, e.g., between two points there can be only one straight line, then no further mark of truth can be given for them than what they themselves express. But all judgments, indeed all comparisons, require a reflection, i.e., a distinction of the cognitive power to which the given concepts belong.