Kant's philosophical career reflects the breadth of his teaching and his interests. When, after 1770, he finally came to write the works for which he is most famous, namely the three Critiques, he addressed what he saw as the fundamental questions that cover human concerns: 'what can I know?', 'what ought I do?' and 'what may I hope for?'. His answers to these questions is marked by the changes he bequeathed to epistemology, ethics and aesthetics. Writing in the Critique of Pure Reason, Kant himself described these changes as a 'Copernican Revolution'. Some of his many other works focus upon the consequences of these foundational revolutions for moral behaviour, law, physical science and religious belief.
Kant's philosophy is set against that of David Hume's empiricism and Gottfried Leibniz's rationalism. In the Critique of Pure Reason, Kant tries to overcome both of these positions and forge a philosophy suitable for the Enlightenment, an intellectual movement that took inspiration from the success of science in the preceding two centuries, and from the decline in the power of the Church. This optimistic age of philosophy held to individual autonomy and freedom of choice, believing that political freedom could follow intellectual freedom. Sapere aude! ('dare to know') was the motto that Kant gave in What is Enlightenment?.
Kant was born and lived all his life in the town of Königsberg (present-day Kaliningrad). His childhood was uneventful, chiefly marked by a Pietistic family background. At school, he mainly learnt theology and the classics, and was particularly fond of Lucretius. He only discovered the exact sciences, mathematics and philosophy upon entering the University at the age of sixteen. He soon settled upon the idea of pursuing an academic career in the exact sciences, and indeed, he was awarded a doctorate for a thesis 'About Fire' (1755). A year later, Kant started teaching at the university, finally obtaining a chair in philosophy in 1770. Although philosophy had become the focus of his research, he taught an impressive range of subjects: mathematics, anthropology, natural sciences, physical geography, logic, metaphysics, moral philosophy, natural theology, fortification construction and pyrotechnics.
As an individual, Kant was a very sociable man who enjoyed regular meals with a number of intellectual but non academic friends. This number was always at least three (the number of Graces) and never more than 9 (the number of Muses). The conversation at Kant's table spanned a broad range of topics, and Kant always showed a keen interest in the latest political, economic and scientific developments. He was known for his wit and his memory for detail, so that he could expound at length upon the impression made by a foreign town, even though he had never visited it.
Kant's early writings are characterised by an important scientific publication, that of Kant's cosmological theory in Theory of the Heavens (1755). Here, Kant is the first to attempt to give a completely mechanistic explanation of the formation of the solar system and more generally of the whole universe on Newtonian principles. Kant leaves no place for any divine intervention in the process. This theory was later validated by Laplace's calculations, and is now known as the Kant-Laplace theory.
A second important characteristic of the writings prior to 1770 is the particularity of Kant's contribution to the metaphysical debates of the day. This is chiefly one of debunking flawed metaphysical constructions which rely upon mere logic (in its Aristotelian form) to derive substantial conclusions about the world, God and the soul. In 1763, he thus publishes 'An attempt to introduce the concept of negative quantities into science'. This treatise seeks to identify internal contradictions in abstract metaphysical theories derived from pure logic. Essentially, Kant points out that, although in logic either A or not-A is true, in reality, something can be both A and not-A. For instance, a body can be both in motion and still since it depends with respect to what point of reference the position of the body is measured.
Among the other topics dealt with by Kant, is the examination of the nature of causality and the proofs for the existence of God. In dealing with causality, Kant, announcing famously that Hume had 'awoken him from his dogmatic slumbers', takes on board much of Hume's scepticism by pointing to the difference between the necessity which connects the conclusion to the premises it is logically derived from, from the necessity connecting a cause and an effect.
In Religion within the bounds of reason, (1793) Kant introduces a notion of faith which is grounded in reason. Since happiness is not fully achievable in the empirical world, it is rational for the moral agent to postulate an endless progress towards it, and that requires the immortality of the soul. The progress implied by a convergence towards the Highest Good, in turn requires an original good, the existence of God as ultimate cause of the natural world.
Kant distances himself from the ritualistic dimension of religion to emphasise the primacy of a religion centred around morality. Although this may involve beliefs in historical facts (such as the resurrection of Christ), religion ought not require more of people than that they behave morally. This understanding of religion was clearly not to the liking of the Prussian Protestant church. Under pressure from Friedrich-Wilhelm II's, Kant agreed to abstain from further expressing his opinions on the subject of religion.
Proofs of the existence of God
The three proofs of the existence of God which were common currency in the metaphysical treatises of the day, were examined by Kant. In these proofs, God is viewed as the ultimate Cause of things (cosmological proof), as a Being whose existence can be deduced from the perfection of the universe He created (the physico-theological proof or argument from design), or as a Being whose existence is necessary in light of the perfection which characterises Him (The ontological proof or ontological argument). These writings, prior to Kant's so-called 'critical turn'. allow it to be at least possible that a combination of the ontological and the physico-theological proofs should enable the construction of a 'well-grounded' demonstration of the existence of God, since the existence of such a necessary being can be argued to be required by the world.
These two issues of causality and the existence of God are interesting as they illustrate the transitional nature of Kant's pre-critical writings. He is taking on board some of the scepticism which originates in British Empiricism (in particular Hume), but is still very much anchored in the metaphysical tradition. However, what is determining for the Critical turn of his thought is the chasm which becomes more and more apparent between the success of a scientific understanding of the world and the unresolved nature of all the speculations of the metaphysicians. Kant is particularly well placed to be aware of this chasm as he is at the forefront of the science of the day (and particularly impressed by the success of Newtonian physics), and wrote extensively about diverse shortcomings of the use of pure logic in metaphysical enquiry.
The 'Critical Turn'
The first publication which indicates the change in Kant’s approach to philosophy known as ‘the Critical Turn' is his inaugural Dissertation (1770) as professor at the University of Königsberg. In this, he identifies the problem of knowledge as that of accounting for the possibility of what he terms 'synthetic a priori' truths. Synthetic judgements are ones such as 'bachelors usually live longer than married men' and are informative, unlike logical statements such as 'bachelors are unmarried men'. A priori statements such as '2 + 3 = 5' are known to be true independently of experience. Another feature of them is that saying the opposite is absurd or self-contradictory. The problem with statements such as 'all events have a cause' is that it makes an a priori claim that holds universally, although it cannot be derived from mere conceptual analysis. Prior to 1770, metaphysicians had happily written treatises full of such claims. Kant was now questioning the validity of the arguments they used.
Kant used mathematics as the paradigm of synthetic a priori knowledge. In geometry, the drawing of a triangle in the mind's eye generates what Kant calls an intuitive representation. Such intuitions constructed under the guidance of a concept (like that of a triangle) form the basis for the acquisition of mathematical knowledge through the formulation of judgements about these concepts. The case of scientific knowledge may prima facie seem quite different as we have to apply concepts to what is in the outside world.
This is where Kant makes what he describes as the 'revolutionary' move of suggesting that, since little success has been reaped from attempting to account for knowledge as conforming to the objects of our experience, it may be more promising to consider these objects as having to conform to our cognitive faculties. This so-called Copernican Revolution in philosophy amounts to a radical rethink of what it is to be an object. For an object is therefore defined in terms of a subject of knowledge. The Critique of Pure Reason (1781) examines the fruitfulness of this approach, and provides grounds for the metaphysical position it represents, Transcendental Idealism.
In this work which, Kant himself confessed, is difficult (and which he substantially revised for the second edition of 1788), Kant examines in detail how synthetic a priori knowledge is possible. The conditions for cognition are of two types: intuitions and concepts. In both cases, there are a priori versions of these. In the case of intuitions, by claiming that space and time are forms of our sensibility that are prior to any experience, Kant is providing a justification for transcendental idealism. For this entails that what we perceive are appearances. By this, he is not suggesting that our perception is in some sense illusory, but rather that what we know is partly the product of our own manner of perceiving.
The concepts that we require 'prior to experience' are categories and their seat is the faculty of the understanding. An object of knowledge is constituted by the application of such categories to a diversity that is given in space and time, thus bringing unity to it. In the case of mathematics, this diversity is generated by the subject thinking under a given concept (for example, that of a triangle). In the case of empirical knowledge, that which is presented in space and time originates outside the subject. Thus, in viewing the movement of a piece of iron towards a magnet as caused by the latter, I am bringing the diversity I perceive under the unity of the category of causality. The objective structure of the empirical world is thus that which I bring to it by applying certain basic concepts.
The faculty of reason is the cognitive faculty which brings further unity to the empirical knowledge acquired by the understanding. The ordering which reason introduces in the diversity of specific elements of knowledge (e.g. Newton's theory of universal attraction) is driven by its search for unconditioned knowledge. The errors of metaphysics consist in assuming reason can obtain the unconditioned. These take three generic forms: knowledge of oneself as a substantial soul, of the world as a totality (for example, whether it has a beginning), and of God (for example, that God exists). Metaphysics makes knowledge claims although it does not respect the conditions for knowledge, which are that some diversity be unified in intuition under a category. By pointing out the source of the errors of metaphysics, Kant seeks to put a full stop after a whole era in the history of metaphysics.
The Categorical Imperative
But he also points to the vocation of reason as lying not in knowledge, but in the practical domain. In the Groundwork to the Metaphysics of Morals (1785), and later, the Critique of Practical Reason (1786), Kant extends this 'Copernican Revolution' to the practical realm. Morality is not connected with the inclinations that are we are subjected to as a result of our empirical nature. Rather, our duty is to give ourselves the law of our conduct, that is to say, to be autonomous. By reflecting upon what could stand as universal duty for any rational agent, Kant derives the famous formula of the categorical imperative: Act only on a maxim that you can at the same time will to be a universal law.
This formula is intended to demonstrate that what is crucial is not the success of the outcome of an action, but the intention formed in acting. This does not mean that consequences are irrelevant, since they are precisely that which has to be weighed up when assessing the moral worth of a purported form of action. But, once a maxim of action is formed that is universalisable, one's duty is fulfilled by acting upon it on the ground of this universalisability.
The way in which this is to be applied can be illustrated by considering the case of the duty not to make false promises. We are asked to consider a world in which the practice of making false promises when convenient is a universal law. In such a world, the institution of promise-making would collapse insofar as no-one would trust any promise-making. The question is then whether we could will such a state of affairs. The fact that we could not is not to be understood as motivated by self-interest, for the only motive here must be duty. Rather, the problem lies in the contradiction there is for someone who universalises a maxim of making false promises when convenient. For he will only be in a position to derive any advantage from breaking his promise if the practice of promise-making is alive and well, which will not be the case if the maxim of making false promises when convenient is universalised. That is, this agent would both will the existence of the institution of promise-making and will a situation in which it cannot exist. This contradiction entails that it is not possible to universalise the maxim in question, so that the maxim of not making false promises is morally binding.
Much as the categorical imperative is sometimes associated with a form of 'rigorism' connected with Kant's Prussian upbringing, it can hardly be said to tie down to agent to precise forms of action. The duty to provide help when needed, for instance, can be implemented in a variety of ways. But it does appear to unconditionally exclude certain forms of action, such as lying, in ways which we might find unacceptable in the face of the complexity of moral life.
Good intentions are enough
In the Groundwork of the Metaphysics of Morals, Kant writes:
Even if, by some especially unfortunate fate or by the niggardly provision of stepmotherly nature, this will should be wholly lacking in the power to accomplish its purpose, if with the greatest effort it should yet achieve nothing, and only the good will should remain (not to be sure, as a mere wish, but as the summoning of all the means in our power), yet would it, like a jewel, still shine by its own light, as something which has full value in itself. Its usefulness or fruitfulness augment nor diminish this value.
There are indeed certain passages in Kant's texts which suggest such an interpretation. We thus find him (considering the possibility of lies prompted by altruistic motives) declaring that a servant's lying to the murderer at the door about his master's being at home, is morally forbidden - even though telling the truth would put the master in mortal danger. Kant also seems to bring apparently irrelevant factors into consideration into the argument, suggesting that there may be circumstances enabling the master to escape, and that, were the master to be killed because, unbeknownst to the servant, he had actually gone out and subsequently encountered the murderer, the servant could rightly be accused of being responsible.
Many rigid interpretations of the categorical imperative however follow from considering simplified examples of moral choices and extending them without clear warrant to more complex cases. That Kant himself was not blind to the complexity of moral issues can be seen by looking at how he deals in detail with practical problems in the Metaphysics of Morals. Thus, in dealing with the tradesman who is honest from self-interest (Groundwork to the Metaphysics of Morals), or in describing avarice or beneficence (Metaphysics of Morals), he shows us how aware he was of the variety of subtle moral distinctions which make up the fabric of our lives.
The dominant role of reason in morality does not however stand in opposition to human inclinations merely for the sake of crushing them. On the contrary, Kant recognises the drive to seek happiness and does not condemn it, as long as it does not take the driving seat in determining human conduct. Indeed, he sees the notion of Highest Good in which happiness accrues to those who act dutifully and in proportion to their so doing, as providing the dutiful agent with a goal for his endeavours.
Kant's Critique of Judgement'
Kant's critical work was not over after the publication of the critiques of pure and of practical reason. For the unity of Kant's system required that the ground of appearance which lies beyond the realm of the knowable, be connected with the intelligible world in which the moral subject exercises his autonomy. This issue is the motivation behind the Critique of Judgement (1790). His solution is found in the examination of the notion of 'purposiveness'.
This says that the unity of our knowledge of the natural world is guided by the idea that it is as though nature had a purpose. It is this idea that accounts for the way in which scientific knowledge is meant to evolve towards an ever greater integration of disparate bodies of knowledge. This teleological grasp of the natural world can then be brought together with the teleological notion of the Highest Good in morality. The purpose of the natural world becomes something that can only be fulfilled through the moral agent.
The judgement that something is 'purposive' can however mean one of two things. It is either that the object is indeed viewed as though there were some objective purpose at work, and this leads to the kind of judgements that characterise our grasp of living organisms for instance. Or it is the judgement that the way in which something is presented is purposive for our cognitive faculties. Typical of the latter is the aesthetic judgement that something is beautiful. By that is meant that what is presented enables a harmony between my imagination and my understanding, as though it were destined for my appreciation. To say something is beautiful is therefore not to bring it under a concept, so there are no canons of beauty. Rather, it is to indicate that the presentation has a form which is particularly adapted to my being able to find structure in it. It is the purposiveness that I judge to be present in the presentation of the rolling hills before my eyes, which grounds my judgement that they are beautiful.
List of Kant's works
Kant was a voluminous writer, which partly explains his considerable influence on the history of thought. Here is a list of his works , spanning not only philosophyin the contemproary sense but the natural sciences and humanities as well.
- (1746) Thoughts on the True Estimation of Vital Forces (Gedanken von der wahren Schätzung der lebendigen Kräfte)
- (1755) A New Explanation of the First Principles of Metaphysical Knowledge (Neue Erhellung der ersten Grundsätze metaphysischer Erkenntnisse; Doctoral Thesis: Principiorum primorum cognitionis metaphysicae nova dilucidatio)
- (1755) Universal Natural History and Theory of Heaven (Allgemeine Naturgeschichte und Theorie des Himmels)
- (1756) Monadologia Physica
- (1762) The False Subtlety of the Four Syllogistic Figures (Die falsche Spitzfindigkeit der vier syllogistischen Figuren)
- (1763) The Only Possible Argument in Support of a Demonstration of the Existence of God (Der einzig mögliche Beweisgrund zu einer Demonstration des Daseins Gottes)
- (1763) Attempt to Introduce the Concept of Negative Magnitudes into Philosophy (Versuch den Begriff der negativen Größen in die Weltweisheit einzuführen)
- (1764) Observations on the Feeling of the Beautiful and Sublime (Beobachtungen über das Gefühl des Schönen und Erhabenen)
- (1764) Essay on the Illness of the Head (Über die Krankheit des Kopfes)
- (1764) Inquiry Concerning the Distinctness of the Principles of Natural Theology and Morality (the Prize Essay) (Untersuchungen über die Deutlichkeit der Grundsätze der natürlichen Theologie und der Moral)
- (1766) Dreams of a Spirit Seer (On Emanuel Swedenborg|Emmanuel Swedenborg ) (Träume eines Geistersehers)
- (1770) Inaugural Dissertation (De mundi sensibilis atque intelligibilis forma et principiis)
- (1775) On the Different Races of Man (Über die verschiedenen Rassen der Menschen)
- (1781) First edition of the Critique of Pure Reason  (Kritik der reinen Vernunft )
- (1783) Prolegomena to any Future Metaphysics  (Prolegomena zu einer jeden künftigen Metaphysik)
- (1784) " What Is Enlightenment?|An Answer to the Question: What Is Enlightenment? " (Beantwortung der Frage: Was ist Aufklärung? )
- (1784) Idea For A Universal History With A Cosmopolitan Purpose (Idee zu einer allgemeinen Geschichte in weltbürgerlicher Absicht)
- (1785) Groundwork of the Metaphysics of Morals (Grundlegung zur Metaphysik der Sitten)
- (1786) Metaphysical Foundations of Natural Science (Metaphysische Anfangsgründe der Naturwissenschaft)
- (1787) Second edition of the Critique of Pure Reason  (Kritik der reinen Vernunft )
- (1788) Critique of Practical Reason  (Kritik der praktischen Vernunft )
- (1790) Critique of Judgement (Kritik der Urteilskraft )
- (1790) The Science of Right 
- (1793) Religion within the Limits of Reason Alone (Die Religion innerhalb der Grenzen der bloßen Vernunft) 
- (1795) Perpetual Peace  (Zum ewigen Frieden )
- (1797) Metaphysics of Morals (Metaphysik der Sitten)
- (1798) Anthropology from a Pragmatic Point of View (Anthropologie in pragmatischer Hinsicht)
- (1798) The Contest of Faculties  (Der Streit der Fakultäten )
- (1800) Kant's Logik|Logic (Logik)
- (1803) On Pedagogy (Über Pädagogik )
- (1804) Opus Postumum
A large part of an early version of this article was taken with permission from the entry By Chris Onof on Kant in 'Essentials of Philosophy and Ethics', edited by Martin Cohen, (Hodder Arnold 2006) and donated to the Citizendium by the authors.
- from the entry on Kant by Chris Onof in 'Essentials of Philosophy and Ethics', edited by Martin Cohen, Hodder Arnold 2006 p151.
- Sapere aude coming from Horace in Epistularum liber primus (the First Book of Letters).
- from the entry on Kant by Chris Onof in 'Essentials of Philosophy and Ethics', edited by Martin Cohen, Hodder Arnold 2006 p154.
- from the entry on Kant by Chris Onof in 'Essentials of Philosophy and Ethics', edited by Martin Cohen, Hodder Arnold 2006 p154.
- sourced from the Wikipedia articxle on Kant, accessed November 20th 2008