Immanuel Kant (1724-1804) is one of the most influential philosophers in the history of Western philosophy. His contributions to metaphysics, epistemology, ethics, and aesthetics have had a profound impact on almost every philosophical movement that followed him.
Kant was born in Königsberg, Prussia, and died in the same city on the Baltic sea. A common myth is that he never traveled more than 16 kilometres from Königsberg his whole life. In fact, between 1750 and 1754 he worked as a tutor (Hauslehrer) in Judtschen, approximately 20 km from his hometown, and in Groß-Arnsdorf (now in Poland, approximately 145 km away).
Kant was born into a family of Lutheran Protestant faith. He was brought up in a Pietist household that stressed religious devotion, humility, and a literal interpretation of the Bible. His education was strict, punitive and disciplinary, and focused on Latin and religious instruction over mathematics and science. In his work Groundwork of the Metaphysic in Morals, Kant reveals a belief in human immortality as the necessary condition of our continued approach to the highest good possible. However, as Kant was skeptical about some of the arguments used prior to him in defence of Theism and maintained that human understanding is limited and can never attain knowledge about God or the soul, most commentators have labeled him a philosophical agnostic.
If one had to summarise Kant's philosophy, one could say he argued that the human mind creates the structure of human experience, that reason is the source of morality, that aesthetics arises from a faculty of disinterested judgment, that space and time are forms of human sensibility, and that the world as it is "in-itself" is independent of man's concepts of it.
A large part of Kant’s work addresses the question “What can we know?” The answer, if it can be stated simply, is that our knowledge is constrained to mathematics and the science of the natural, empirical world. It is impossible, Kant argues, to extend knowledge to the supersensible realm of speculative metaphysics. The reason that knowledge has these constraints, Kant argues, is that the mind plays an active role in constituting the features of experience and limiting the mind’s access only to the empirical realm of space and time.
Kant responded to his predecessors by arguing against the Empiricists that the mind is not a blank slate that is written upon by the empirical world, and by rejecting the Rationalists’ notion that pure, a priori of a mind-independent world was possible. Reason itself is structured with forms of experience and categories that give a phenomenal and logical structure to any possible object of empirical experience. These categories cannot be circumvented to get at a mind-independent world, but they are necessary for experience of spatio-temporal objects with their causal behavior and logical properties. These two theses constitute Kant’s famous transcendental idealism and empirical realism.
Kant’s contributions to ethics have been just as substantial, if not more so, than his work in metaphysics and epistemology. He is the most important proponent in philosophical history of deontological, or duty based, ethics. In Kant’s view, the sole feature that gives an action moral worth is not the outcome that is achieved by the action, but the motive that is behind the action. And the only motive that can endow an act with moral value, he argues, is one that arises from universal principles discovered by reason. The categorical imperative is Kant’s famous statement of this duty: “Act only according to that maxim by which you can at the same time will that it should become a universal law.”
Kant's political thought can be summarized as republican government and international organization. In more characteristically Kantian terms, it is doctrine of the state based upon the law and of eternal peace. Indeed, in each of these formulations, both terms express the same idea: that of legal constitution or of 'peace through law'. Taken simply by itself, Kant's political philosophy, being essentially a legal doctrine, rejects by definition the opposition between moral education and the play of passions as alternate foundations for social life. The state is defined as the union of men under law. It is constituted by laws which are necessary a priori because they flow from the very concept of law. A regime can be judged by no other criteria nor be assigned any other functions, than those proper to the lawful order as such. Kant's "Perpetual Peace: A Philosophical Sketch," is considered to have foreshadowed many of the ideas that have come to form the democratic peace theory.
Nevertheless, Kant is perhaps best known for his theory of perception. He asserts that experience is based both on the perception of external objects and a priori knowledge. The external world, he writes, provides those things that we sense. But it is our mind that processes this information and gives it order, allowing us to comprehend it. Our mind supplies the conditions of space and time to experience objects. According to the "transcendental unity of apperception", the concepts of the mind (Understanding) and the perceptions or intuitions that garner information from phenomena (Sensibility) are synthesised by comprehension. Without the concepts, perceptions are nondescript; without the perceptions, concepts are meaningless — thus the famous statement, "Thoughts without content are empty, intuitions (perceptions) without concepts are blind."
Kant also claims that an external environment is necessary for the establishment of the self. Although Kant would want to argue that there is no empirical way of observing the self, we can see the logical necessity of the self when we observe that we can have different perceptions of the external environment over time. By uniting all of these general representations into one global representation, we can see how a transcendental self emerges. "I am therefore conscious of the identical self in regard to the manifold of the representations that are given to me in an intuition because I call them all together my representations."