Immanuel Kant, like Plato and Aristotle, counts as one of the most influential philosophers of all time. He developed a new theory of time and space that combined insights from rationalism and empiricism. In his practical philosophy he developed a completely new approach, which makes Kant one of the most distinguished scholars of the European Enlightenment.
Kant was born in Königsberg (formerly East Prussia, since 1945 renamed Kaliningrad, Russia) on April 22, 1724, as the son of a saddler. He was brought up in the spirit of Pietism, a Lutheran movement that focused on love, which is realized through duty and good deeds. He never left Königsberg. It was there where he went to school and attended university, where he received permission to teach as a university lecturer (Privatdozent) in 1755, and again where he was appointed full professor of logic and metaphysics in 1770 after declining an offer from Jena in 1769. He held this position for the rest of his life and died on February 12, 1804.
The tone of the German intellectual landscape in which Kant started his work was largely set by the so-called “school philosophy” of Leibniz and Wolff, a thoroughgoing form of rationalism. Wolff, continuing Leibniz's work, believed that every truth of reason could be deduced from the principles of noncontradiction and sufficient reason. When Kant encountered Hume's empiricist philosophy, he felt awakened from his dogmatic slumbers. In 1770 he consolidated many of the intellectual gains he had made during the 1750s and 1760s in his Latin inaugural dissertation (Habilitationsschrift). He introduced an important new theory about the epis-temology and metaphysics of time (and space). His fundamental new philosophical insight, which he later elaborated in his famous work Critique of Pure Reason, goes as follows:
1. The idea of time does not arise from the senses but is presupposed by the senses. … 5. Time is not something objective and real (tempus non est obiectivum aliquid et reale); it is neither an accident, nor a substance, nor a relation; it is the subjective condition, necessary because of the nature of human mind, of coordinating everything that we experience (quaelibet sensibilia) by a certain law, and is a pure intuition. For we coordinate substances and accidents alike, as well according to simultaneity as to succession, only through the concept of time.
The same holds for space, which he maintains is also neither objective nor real. Kant combines Hume's empiricist point of view with the rationalistic assumption of an ordered universe. Hume believes that with sense-knowledge, the given consists of impressions and sensations, and, for this reason, we can only discover post hoc a succession in time without causal relation. Rationalists assume that there is a fundamental causal connection between events (a post hoc principle of sufficient reason). Kant explains that time and space, as our subjective forms of intuition, are the reason why we have the experience of causal connections without holding that these causal connections are real in an absolute sense. But they are real to us, because all human beings have the same experience, which results from the notion that all human beings have the same subjective forms of intuition; that is, of time and space. Kant's position on time and space is of great philosophical interest. For example, Einstein's theory of relativity shows that it is not possible for us to have absolute time or space, so it seems to be true that our experiences are just of appearances and do not tell the whole story.
In his Critique of Pure Reason (1781/1787) Kant developed these important insights to encompass all the categories used in thought. However, Kant admits that this work does not describe the whole system but instead is the blueprint for a new transcendental philosophy, thereby destroying the metaphysics of the past. Kant's central idea is to argue that the unity of consciousness, the so-called transcendental unity of apperception, categorizes all of the sensations according to the forms of intuition (time and space) and the forms of intellect; that is, the pure concepts (categories). This explains why there are universal and necessary laws for every being with consciousness and intellect, in other words, for every human being. Kant calls this knowledge synthetic a priori, because it is necessary and universal, on the one hand, but is not inferable through the analysis of concepts, on the other. From that follows that “things” that are not explicable in space and time, for example, God or an immortal soul (if they exist), cannot be assessed by human beings without leading to an endless series of irresolvable disputes. The previous system of metaphysics is now null and void. As a result, we cannot derive ethical conclusions from theological (or metaphysical) “knowledge” of the good. We are left without a solid foundation for a consequentialist account of ethical reasoning.
Kant proposes an alternative theory of practical reasoning that can be found in Fundamental Principles of Metaphysics (1785), Critique of Practical Reason (1788), The Metaphysics of Morals (1797), and numerous sections of other works. He assumes that only a will that acts for the sake of duty and not for the sake of inclination is a morally good will. The will is good when, for the sake of duty, it follows the fundamental commandment he calls the “categorical imperative,” a principle of action that is a universal moral law. All rational beings endowed with freedom, regardless of their particular interests and social background, have to adopt this principle. Kant formulates it in the Groundwork for the Metaphysics of Morals in four different ways. The most famous formulation is as follows: “Act only according to the maxim (the determining motive of the will) through which you can at the same time will that it become a universal law.” By universal law Kant means that this principle does not allow for exceptions, in contrast to the laws of nature. Another formulation of the categorical imperative demands the impartial respect of humanity in every human being: “Treat humanity … never simply as a means, but always at the same time as an end.” Here Kant introduces the concept of human dignity, which remains among the most discussed of all ethical concepts.
In his third critique, the Critique of Judgement, Kant tries to unite theoretical and practical reason. Nature can be understood as a determinate system only under the regulative idea of being a system serving an ultimate end. This idea is regulative because it helps us to understand nature according to our capacities of reason. Consequently, we do not know whether nature serves an ultimate end at all; instead we are just left to postulate it.
Many aspects of Kant's theoretical and practical philosophy have been questioned, in particular his assumption of synthetic a priori propositions and his ethics of the categorical imperative. His theory of time and space, however, will likely remain a cornerstone of philosophical thought for generations to come.
Ethics, Hume, David, Intuition, Metaphysics, Morality, Space, Space and Time, Time, Perspectives of
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