Immanuel Kant was an 18th-century German philosopher from the Prussian city of Konigsberg. Kant was the last influential philosopher of modern Europe in the classic sequence of the theory of knowledge during the Enlightenment beginning with thinkers John Locke, George Berkeley, and David Hume.
Hume gave an analysis of causality that made the application of the concept of causality to reality extremely problematic. Because of his empirical insistence that we know through experience, it was natural for Hume to notice that what we call causal relationships were nothing other than constant conjunctions of events: one thing after another in regular fashion. Like the frames of a movie film, we see one thing and then another, but we never get to see what happened in between; there is a natural limitation on what we can know about causality. We cannot know from experience that there is a causal relationship actually present.
This encounter with Hume stunned Kant out of what he later described as his "dogmatic slumber." In practice, this means comfortable engagement with the thought world of continental rationalism (especially Leibniz and Wolff). But why? What was at stake in Hume's analysis that so alarmed Kant?
First, Newtonian mechanics depended on the idea of causality. If causality could not be known to be metaphysically real, then Newtonian mechanics could not be given a rational philosophical foundation. In fact, any attempt to discern laws of nature would be undermined, because the application of laws depends on causality. All of pure natural science was in danger from Hume's argument.
Second, if Hume was right about causality, then maybe other metaphysical concepts were in danger in parallel ways. For example, how could we know if there is unity or plurality in the world? We experience apparent pluralities of things with unified characteristics (e.g. being), but how can we justify our traditionally confident knowledge that things in the world are as they appear to us?
Third, if those mundane metaphysical concepts are in danger of being placed beyond the reach of our knowledge, then what about ideas that are important for the moral life, such as God, freedom and immortality? What about the idea of "self" or the idea of "world"?
Kant's solution to these problems can be thought of as two-fold.
First, in a kind of damage control move, he intensified Hume's critique by trying to find out every last concept that was affected by the kind of argument that Hume advanced about causality, and offering an argument that there were no more.
Second, Kant developed an extended theory about how the human person knows, with a view to determining precisely what can be known and what cannot be known, as well as a categorization of the kinds of knowledge that can be had.
The first step in both parts of Kant's answer to Hume was a theory of judgments.
The Copernican Revolution, which in terms of astronomy amounted to the acceptance of heliocentrism as suggested by Nicolaus Copernicus, has also been used widely as a metaphor supporting descriptions of modernity. A particularly prominent case was the selection of this comparison by Immanuel Kant in his Critique of Pure Reason to explain the effect in epistemology of his new transcendental philosophy.
The attribution of the comparison with Copernicus to Kant himself is based on an passage in the Preface to the second edition of the Critique of Pure Reason (1787, and a heavy revision of the first edition of 1781). In an English translation, it begins:
"Hitherto it has been assumed that all our knowledge must conform to objects. But all attempts to extend our knowledge of objects by establishing something in regard to them a priori, by means of concepts, have, on this assumption, ended in failure. We must therefore make trial whether we may not have more success in the tasks of metaphysics, if we suppose that objects must conform to our knowledge. This would agree better with what is desired, namely, that it should be possible to have knowledge of objects a priori, determining something in regard to them prior to their being given. We should then be proceeding precisely on the lines of Copernicus' primary hypothesis. Failing of satisfactory progress in explaining the movements of the heavenly bodies on the supposition that they all revolved round the spectator, he tried whether he might not have better success if he made the spectator to revolve and the stars to remain at rest. A similar experiment can be tried in metaphysics, as regards the intuition of objects".
Much has been said on what Kant meant by referring to his philosophy as 'proceeding precisely on the lines of Copernicus' primary hypothesis'. There has been a long standing and unresolved discussion on the inappropriateness of Kant's analogy because, as most commentators see it, Kant inverted Copernicus' primary move. This inversion is explained below by Victor Cousin,
"Copernicus, seeing it was impossible to explain the motion of the heavenly bodies on the supposition that these bodies moved around the earth considered as an immovable centre, adopted the alternative, of supposing all to move round the sun. So Kant, instead of supposing man to move around objects, supposed on the contrary, that he himself was the centre, and that all moved round him."
Put simply, the 'inappropriateness of the comparison' is suggested because Copernicus' revolution declared that earth moved around heavenly bodies, instead of heavenly bodies moving around earth. But in Kant's metaphysical revolution this move appears reversed. He declares a situation akin to bodies moving around man instead of man moving around bodies.
But a third component of this analogy has been overlooked-that of light. Copernicus found our illuminating sun central in his inquiry into astronomy. Likewise in Kantian philosophy, the synthesizing subject is central because it is the subject who draws the world from obscurity by coordinating content into things, thus producing phenomenological experience, i.e. vision. Reading this metaphorically, the subject illuminates the world. So Kant duplicates Copernicus' original revolution, since the light of the world is again declared the center of the world. As simply as Copernicus interchanged the position of the earth with the sun in astrological discourse, Kant sublimates the spectator with the stars, and revolution is born.
According to Tom Rockmore, Kant himself never used the "Copernican Revolution" phrase about himself, though it was "routinely" applied to his work by others.
Religion and scientific picture of the world.
Kant stated the practical necessity for a belief in God in his Critique of Practical Reason. As an idea of pure reason, "we do not have the slightest ground to assume in an absolute mannerâ€¦ the object of this ideaâ€¦", but adds that the idea of God cannot be separated from the relation of happiness with morality as the "ideal of the supreme good." The foundation of this connection is an intelligible moral world, and "is necessary from the practical point of view".The reality of the idea of God can only be proved by means of this idea, and hence only with a practical purpose, i.e., to act as though there is a God, and hence only for this purpose" .
Along with this idea over reason and God, Kant places thought over religion and nature, i.e. the idea of religion being natural or naturalistic. Kant saw reason as natural, and as some part of Christianity is based on reason and morality, as Kant points out this is major in the scriptures, it is inevitable that Christianity is 'natural'. However, it is not 'naturalistic' in the sense that the religion does include supernatural or transcendent belief. Aside from this, a key point is that Kant saw that the Bible should be seen as a source of natural morality no matter whether there is/was any truth behind the supernatural factor. Meaning that it is not necessary to know whether the supernatural part of Christianity has any truth to abide by and use the core Christian moral code.
Kant articulates in Book Four some of his strongest criticisms of the organization and practices of Christianity that encourage what he sees as a religion of counterfeit service to God. Among the major targets of his criticism are external ritual, superstition and a hierarchical church order. He sees all of these as efforts to make oneself pleasing to God in ways other than conscientious adherence to the principle of moral rightness in the choice of one's actions. The severity of Kant's criticisms on these matters, along with his rejection of the possibility of theoretical proofs for the existence of God and his philosophical re-interpretation of some basic Christian doctrines, have provided the basis for interpretations that see Kant as thoroughly hostile to religion in general and Christianity in particular.
There is a well-established image for the relationship between religion and science - an image not of head-to-head conflict, but rather of a kind of benign independence the one from the other. Immanuel Kant, the 18th century philosopher, first captured this image. Science, he said, is sovereign in the pursuit of fact; religion is sovereign in the pursuit of value. Science is the means to discovering what is true; religion is the means to discovering and living out what is good. They work in different realms; they come into conflict only when one or the other steps outside the area amenable to its methods.
Kant wanted to defend religion from skeptical arguments and Newtonian science from a similar type of skepticism. He also defended a libertarian theory of human nature from the new determinism that many saw as implicit in Newtonian physics. This is the problem of heteronomy and autonomy. The former is the view that even human behavior is controlled by the same laws as the rest of the universe, implying that free will is an illusion. The latter is the view that not all human actions are dependent on (or deducible from) the laws of nature.
Kant's theory of knowledge was based on a complex theory of categories of the mind that we have a priori and that we apply to experience. Without it we could not have any coherent experience. It constitutes a third way of knowledge between a priori mathematical and logical concepts and those based on experience. It is synthetic a priori knowledge. Just as Copernicus reversed the roles of the sun and earth, so Kant reversed the role of thought and experience: We impose our mental categories on the world, not vice versa.
Kant argued that these concepts applied only to the world of experience and could not apply to metaphysical problems such as God, freedom, and immortality. He produced a complex critique of the three traditional theistic proofs (ontological, teleological, and cosmological) but also argued that reason could not disprove God's existence, and then offered pragmatic proofs for such a belief. Kant's Religion within the Limits of Reason Alone was an attempt to replace religion based on revelation or fideism.
What is most remarkable about the philosophy of Kant, in my opinion, is the wide range of topics on which his thoughts repay careful study. In so many areas - not only in metaphysics but in natural science, history, morality, the critique of taste - he seems to have gone to the root of the matter, and at least raised for us the fundamental issues, whether or not we decide in the end that what he said about them is correct. In his brief, five-page essay on the question "What is Enlightenment?" for example, he locates the essence of enlightenment not in learning or the cultivation of our intellectual powers but in the courage and resolve to think for oneself, to emancipate oneself from tradition, prejudice, and every form of authority that offers us the comfort and security of letting someone else do our thinking for us. Kant's essay enables us to see that the issues raised by the challenge of the Enlightenment are still just as much with us as they were in the eighteenth century.