The professor and the man
Initially tutor at Pasteur of countryside and in various families of the surroundings, it taught, since 1755, in the capacity as Privatdocent (candidate-professor) and, fifteen years later, obtained the title of full professor of logic and metaphysics, thanks to his Essay of 1770, written in Latin (Of the form and the principles of the sensitive world and the understandable world). Consequently, Kant entirely devoted itself, on the one hand, with the development of doctrines deeply contemplated, to which will testify, starting from the Criticism of the pure reason (1781), of original philosopher's stones and, on the other hand, with a teaching which it will exempt with exactitude, during more than forty years and at a rate of five hours per day, until 1797, date on which, feeling his forces to decline, it took leave of faculty to put the last hand at the one of the vastest systems and most strongly constructed of all the history of philosophy.

This work was the fruit of a life regulated with meticulousness. Kant had established itself his timetable with a precision of clock and watch maker: “If I were in the need, the last object that I would sell would be my watch!” One of its familiar, the adviser von Hippel, had of it even drawn a comedy, the Man with the watch (1760). Be like winter, invariably awaked by its servant Lamp at 4:55, he drank two cups of tea, smoked his only pipe of the day and sat down at his office (which he called his anvil). At 7:45, the days when it went to faculty, it started to turn in round; at 7:50, it put on its hat on its head; five minutes later, it took its cane and, with first the 8 hours blow, it opened the door of its car, so that, like noted it its secretary and biographer Jachmann, “it was used truly as clock all to the inhabitants of the district”. The afternoon, the philosopher went for his famous walk, always the same one, which lasted one hour. It was not seen, it is said, that twice in forty years to exceed the limit where it usually stopped: once to have earlier a work of Jean-Jacques Rousseau, the other time to have news of the French revolution.

An encyclopedic spirit
The writer and German philosopher Johann Gottfried Herder, who was the pupil of Kant with Königsberg, had had a luminous memory of his professor, on the subject of which he wrote later that in full maturity “he had this promptness of a young man, that he kept until the most advanced age. Its released face, conformed for the thought, was the seat of imperturbable and merry serenity. It always had shares humor and the spirit of it, and its teaching was the most entertaining maintenance which is”.

It is with same assiduity that Kant studied Leibniz, Wolf, Baumgarten and Hume, the natural laws of Kepler, Newton and the writings of Jean-Jacques Rousseau (Emile and the Héloïse News), as all the new discoveries which reached him. Without party taken, the philosopher sought to look further into his knowledge on nature and the values morals of the man. It was interested as much in the history of the men, the people and nature that to biology, mathematics and the experiment, sources of its teaching and its talks.  

Without interest for the intrigues, the fashionable celebrities, the quarrels of clans and schools, without intellectual despotism either, it sacrificed all in search of the truth: “It woke up and forced gently with an autonomous thought.”  

Three questions of philosophy

Kant was concerned with provide a decisive answer to the three following questions: What can I know? What do I have to make? What is it allowed to me of hopes for R? who par excellence constitute the program of any philosophy.

What can I know?
With the first of these questions, Kant draws aside the dogmatism, which affirms the possibility of reaching a priori (out of any experiment) an absolutely true knowledge, but it rejects also the empiricism skeptical, which absolutely denies such a possibility by affirming that, any knowledge being derived from the experiment, it is particular and contingent.

By the question That can I know? , the philosopher tackles the problem of knowledge under a new angle: instead of admitting or to refuse any species of knowledge absolutely, he seeks the conditions of possibility which make it possible to reach a true knowledge, whose model is provided by science itself (Kant understands by there the mathematical physics of Galileo and Newton). This science exists, its successes prove this fact. But it is the Criticism of the pure reason which gets busy to determine in which conditions it is possible. With this question Kant answers that there can be knowledge only phenomena taking place in space and time. Only these phenomena get for our sensitivity of the intuitions, which constitute the matter of our knowledge and to which we are in relation to the sensitive world.  

Knowledge and the experiment
In a first direction, any knowledge thus starts with the experiment. But that means by no means but any knowledge derives from the experiment. Quite to the contrary, it is the experiment itself which is a priori, in the sense that there is possible experience without the forms a priori of the sensitivity which are precisely space and time. Each one of these terms must be taken in the singular, because there is not, from the point of view of knowledge itself, that a space and that a time, absolutely universal and necessary. “Two different times, written Kant, are necessarily successive.” And the time which “suspends its flight” is only one poetic invention.  

Thus, the “Analytical one” of the Criticism of the pure reason establishes that space and time, forms a priori of the sensitivity, are conditions of the existence of the things, but only like phenomena (or appearances), without we being able to know noumenes (“things in oneself”), of which we do not have null sensory intuition and whose these phenomena are only the demonstrations. Ultimately, there is not other true knowledge, i.e. of science, that of the objects of the experiment. However, this knowledge is far from being purely empirical.  

Transcendental knowledge
So that a knowledge is real, one needs not only intuitions of the sensitivity, of which is occupied transcendental esthetics, but also concepts pure of the understanding, covered by transcendental logic. Kant calls transcendental “any knowledge which deals less with the objects than in our manner of knowing them as this mode of knowledge must be possible a priori”. The pure concepts of the understanding (or categories) cannot be provided by the experiment, since it is them, on the contrary, which make a priori it possible. Kant drew up the systematic table of the twelve categories which apply a priori to the objects of the intuition in general and which group in four classes (1 quantity: unit, plurality, totality; 2 quality: reality, negation, limitation; 3 relation: inherency, causality, community; 4 method: possibility, existence, need).  

Critical philosophy
Thus, we can know really only objects of which our sensitivity provides us an intuition (their matter) and of which our understanding provides the concept (their form). Because “of the intuitions without concepts are blind and the concepts without intuitions are empty”.

For knowledge, the sensitive world is thus at the same time an obstacle and a means. Also, passion (metaphysical) to exceed the sensitive world is long-lived. It nourishes illusion which we can free from gravity of the experiment: “The light dove, when, in its free flight, it splits the air of which it feels resistance, could think that it would succeed well better still in the vacuum. It is precisely as Plato left the sensitive world because this world erects to the understanding too various obstacles, and risked himself beyond this world, on the wings of the ideas, in the vacuum of the pure understanding.”  

To the idea of an absolute knowledge of the objective reality, which gives to place, since Antiquity, a controversy between dogmatic and to skepticals, Kant a new philosophy of knowledge opposes: the critical philosophy, which reverses the report of the subject to the object. It shows that, far from being the simple reproduction, in the spirit of a subject, real nature of an object, true knowledge is relative in its empirical discovery of an object, which has the structure of the subject a priori. “The reason sees only what it produces itself according to its own plans.”  

Thus, just as Copernic made turn the Earth around the Sun, and not the reverse, Kant defines (i.e. founds and limit) knowledge rational to leave either the nature of the object, but of the power to know subject (and limits of this power). The “revolution copernician”, which characterizes critical philosophy, is decisive: contrary to the specific illusion to all dogmatisms metaphysics, a priori - pure concept of the understanding or pure idea - provides alone no knowledge, and metaphysics cannot thus be a science: “I due to abolish the knowledge, known as Kant, to make a place with the belief.” Indeed, it is from now on possible to think as object of belief what it is interdict to know like object of science: it should not any more be believed that one knows but to know that one believes.

What do I have to make?
In critical philosophy, this question come after that from That do I can know? and before that of Which is allowed to me to hope for? This place assigned with the moral problem means first of all that the question of knowledge leaves entirely open that of morals. Kant, indeed, establishes firmly that science of a state of affairs one cannot draw the rules from what must be, not more than I cannot draw from “what is made” (or of “what the others do”) the precepts relative to “what I must do”. However very whole science is restricted to indicate phenomena, while it returns to morals to prescribe actions. Science and morals are thus independent and separately founded, because one cannot draw a requirement from a code.

In addition, the answer to the question Which do I have to make? is completely independent of any hope, of some nature that it is, since it precedes the question Which it is allowed to me to hope for? In other words, the only construction of the work of Kant is enough to suggest that the morals, which occupies the central place in critical philosophy, is independent of science and the religion.  

It the Critic of the practical reason which provides to the question That is I do have to make? an answer, which can be summarized as follows: We must make our duty by pure respect for the moral law, which is registered at the bottom of our hearts, and without awaiting any other reward that satisfaction intimates accomplished duty.

It is the duty, well rather than the right, which constitutes the moral fact par excellence. Belonging physically to the sensitive world, the man belongs morally to the suprasensible world (or understandable) where the “majesty of the duty does not have anything to make with the pleasure of the life”: he is thus citizen of two worlds - that of the nature and that of freedom - and has to live, at the same time like subject and legislator, in the tearing of this double citizenship.  
 The reasonable subject, narrowly limited to the only science (of the phenomena) and limited in its claims to a metaphysical knowledge (To be it), on the other hand is promoted sovereign “legislator” in the moral field (of the duty-being). It is only in this field which he discovers - at the same time as the obligation which is made to him by the “moral law” registered in him a priori - his freedom as a be reasonable.

Obligation and need
Kant establishes a fundamental distinction between what is obligatory and what is necessary. The obligation (moral) should not be confused with the need (physical). While science makes known to us only the need for the phenomena (nature), morals reveals us our own freedom. Inconceivable for the theoretical reason, which subjects all the phenomena to the law of causality, freedom is, on the other hand, for the practical reason, the raison d'être of the duty-being. Because the duty would be a nonsense if we did not have the possibility of achieving it or of us to conceal there, i.e. if we were not free. Morals can be founded, affirms Kant, neither in the sky nor on the Earth: it can be founded only in ourselves, which sums of the be reasonable and free. It is in the sense that freedom is the fundamental postulate of morals.  

What is it allowed to me to hope?
Two other postulates - the existence of God and the immortality of the heart - make it possible to hope that our moral effort falls under a vast plan (hidden) of nature. Thanks to the moral law, we can indeed regard us as free and independent with regard to the physical need, and judge that we are higher, as moral subjects, with whole nature. Consequently, it is allowed to us to hope that, if necessary, we will make our duty (since we can achieve it). In addition, we have to hope that all the other men, in spite of the afflicting table that the history of humanity presents to us, will end up also acting like moral beings, free and reasonable. In this respect, Kant, so near to Rousseau in addition, is however far from sharing the optimism of the author of the social Contract: “The man, Kant writing, were cut in a wood if twisted that one will be able about it to never draw something from completely right.” But that does not change anything with the morals, which is expressed by the categorical imperative: You must! (thus, you can). Without discounting any rewards nor to fear some damage that it either, “acted so that the maxim of your action can be set up in universal moral law”.  

As for the finality of the human actions, Kant affirms that only humanity, as a universal ideal of the reason, is an end in itself: “Acted so that you treat humanity, as well in you as in others, always like an end and never simply like a means.” Thus acting, each one would be “at the same time legislator and subject” of the republic of the ends.  

Other morals of the duty
This concept of the autonomy of the moral subject, by the central place that it occupies in critical philosophy, distinguishes the doctrines from Kant of all other “morals of the duty”, former or posterior, such as, in particular, the Christian morals of charity or morals Marxist-Leninist of the fight of the proletariat against the exploitation of the man by the man. For these morals, the existence is very whole nun or policy: each one has in load all the misery of the world, and no one does not have right at rest as long as there will be in the world of the unhappy one, of the non-believers, the patients, of oppressed, of exploited. The duty to be achieved, for political hello or monk of humanity (heard quantitatively as the sum of all the men), clearly seems there an infinite task, to which the individual must devote himself absolutely and indefatigably. According to these morals of the duty, the individual did not give anything as much as it very did not give.  

Kantian morals
According to Kantian morals, it is necessary and it is enough that each one freely makes its duty specific to the be reasonable, that it achieves it in the place which is reserved for him, however modest it is, so that are dried up with their source violence and the injustice. In this direction, each one is responsible for humanity (heard this time like the properly human quality of our acts): the individual does not have to assume this responsibility by some important fact or sacrifice which to him would be ordered outside (by God or a party), but by the quiet and daily achievement for his tasks.

If the duty appears contrary with nature, and sometimes particularly painful to achieve, it is that humanity is not yet universally regarded as an end. So that, for a morally autonomous subject, which does not miss good will, the major hurdle and truly infernal with the practice of the duty is consisted “the others”, those which, not acting as they should, place, artificially, in situations against nature, of a diabolic perversity: it is what occurs when, for example, somebody is invited by an assassin to denounce, under penalty of death, the hiding-place of a friend that it continues to kill it. Such concrete cases, fortunately exceptional, should not let to us infringe our principles nor of inclining us with the lie. It only remains to be hoped, in fact, that, by refusing us to lie, we will not determine the loss of our friend.

Concepts of finality and beauty

The moral subject thus legislates supremely. However nature (in us and out of us) generally opposes the search for what one names commonly the happiness (which, according to Kant, is only one “ideal of imagination”). It requires sometimes even the sacrifice of our personal interest. But it is enough that she is not opposed absolutely to the agreement of the true happiness with the morality - agreement which constitutes the sovereign well - to be able to admit that the finality is registered in nature and that “nothing exists in vain”.  

Critic of the judgment
To discover this finality by the analysis of the esthetic judgment (which relates to the beautiful one and sublimates it) and of the teleological judgment (which relates to the organization of the living beings), such is the object of the Critic of the judgment. This third work of “philosophy criticizes” roof the interval between the two first. It connects the field of natural causality to that of moral freedom by theoretically reconciling the practice of morality with the ends of nature, in particular thanks to the concept of the finality. Analysis of the esthetic judgment, Kant draws four conclusions: firstly, the beautiful one is the object of a not involved satisfaction; secondly, the beautiful one is what likes universally without concept; thirdly, the beautiful one contains a finality, but without the representation of an end; fourthly, the beautiful one is recognized like the object of a satisfaction necessary.  

The common direction (sensus communis), which is with work in the esthetic and teleological judgments, could not be confused with the reason (Vernunft), although this one also presents a universal character. Admittedly, the “cold reason” is common to all the men, and it constitutes the universal unit of mankind. But the common direction brings something moreover: it reveals, in its turn, that the men belong to a fraternal and hot community, joined together in the subjective perception of the beauty and the finality in nature.

Nature and history
The finality was driven out science, but, initially introduced subjectively by the feeling of beautiful, we find it intact in nature, in particular when we consider the living organisms: those are not only machines holding a driving force, “they have a formative energy which they communicate even to the matters which do not have it and which they organize”.  

This double reading - esthetics and teleological - organization of nature makes it possible to detect a plan hidden in it, and to grant a direction to the history of the humanity, filled however of noise and fury. Indeed, the conditions of possibility exist so that be reasonable and free taste the beauty of the things fully, in particular while agree to live under the only authority of the universal moral law. The rational requirement of the right should thus finally carry it on violence. And this success can be only final, because if nature had wanted the happiness immediate of the individual, it would have equipped it with the instinct and not with the reason. By making us beings of reason and feeling, subjects “of an unsociable sociability”, it organized us for this imposing task which is the institution of humanity.   

The philosophy of Kant is completed thus in a political thought which considers the human history, in spite of appearances, like a field placed under the aegis of morality and opened with the realization of a great intention, namely “the establishment of a civil society managing the right in a universal way”.  

Kantianism

None the philosophers who came after Kant could be unaware of critical philosophy, and all were obligatorily brought to be located compared to the Kantianism.

Initially, Kant is the founder of what it is agreed to call the German idealism, whose three large representatives are Johann Gottlieb Fichte (1762-1814), Friedrich Schelling (1775-1854) and Friedrich Hegel (1770-1831).  

The immediate or remote successors of Kant divided primarily in connection with the statute of “noumene”, the ones regarding it as supreme reality though unknowable according to the Kantianism, the others looking at this “thing in oneself” (Ding year sich) as an entity whose Kantian system could without disadvantage of making the economy. In other words, the project of Kant, is wrongly or rightly perceived sometimes (in particular by positivism) like that of a grave-digger of metaphysics, sometimes (by Bergson) like that of a metaphysician presenting “a hardly renewed Platonism”, or even (with Heidegger) like the ultimate attempt at a refondator of metaphysics.  

In France, the neokantism is mainly represented by the Protestant philosopher Charles Renouvier (1815-1903), who, in its many articles published in philosophical Critique, review founded in 1872, tackles empiricism, the Hegelianism, positivism and places “morality” (with the Kantian direction) above all the historical contingencies.

In Germany, it is the transcendental philosophy of Kant who inspired the phenomenology of Husserl. As for Heidegger, it has, during the winter 1925-1926, suggested an analysis of the Criticism of the pure reason - it will be published in 1929 pennies the Kant title and the problem of the metaphysics - which constitutes a first development of the second part Être and Time. The purpose of the work of Heidegger is to explain the Criticism of the pure reason “as an introduction of the base of metaphysics”. Thus, according to Heidegger, with Kant “the problem of metaphysics is clarified like problem of a fundamental ontology”.  

Sartre itself, if distant that it appears Kantianism, from Kant the essence of his morals borrows obviously, more exactly it poses the moral problem in the properly Kantian terms of the universality: “Any man, he affirms, is responsible for very in front of all.” Moreover, the title even of the work of Sartre Criticizes dialectical reason said enough its debt towards the author of three Criticisms. Indeed, in the existentialism sartrien, the duty remains as imperatively categorical as in Kantian rationalism: “All that I make, written Sartre, is probably dedicated to the failure, but I do it nevertheless because it should be done.”