Since he was born at a time when East Prussia was recovering from the devastation of war and plague, Kant grew up in an atmosphere of poverty. The main influence of his life was his mother a pious, austere, yet loving woman, whose moral character shaped that of her son and played a prominent role in Kant's philosophy.
As a professor at the University of Königsberg, Kant lectured mainly on mathematics and physics, however, his natural inclination was towards philosophy which he began to read and study widely. He read and was much influenced by, the works of the rationalists and empiricists such as Leibniz and Hume. He was also stirred by the emotional writings of Jean Jacques Rousseau, probably considered one of the most non-academic philosophers.
During the course of his readings and study, Kant eventually became critical of many of the rationalist and empiricist principles. While he recognized the strength of the empiricist claim that sense experience is the source of our beliefs, he could not accept the conclusion that those beliefs cannot be justified. He also rejected the rationalist claim that factual truths about what does, and does not exist, can be conclusively established by reason alone. So what can we know and how?
Although Kant was reluctantly convinced of some of Hume's empiricist arguments, he one day "awoke from his dogmatic slumbers" and in a flash of inspiration envisioned how he could construct a system in response to what he considered to be Hume's destructive skepticism. It came in the form of his most important work Kritik der reinen Vernunft or Critique of Pure Reason.
While Kant agreed with Hume and the empiricists that there are no such things as innate ideas, he denied that all knowledge is derived from experience. In a brilliant reversal of self-proclaimed Copernican proportions, Kant argued that all experience must conform to knowledge. Taking a revolutionary position, he maintained that the mind is active and plays a part in shaping the world of experience. In other words, instead of knowledge consisting in our minds and conforming to a world of objects, Kant maintained that objects must conform to our minds. Thus, the mind plays a part in the nature of the empirical world. He also made the point that there is a distinction between appearances (phenomena) and things in themselves apart from experience (noumena).
Kant's second work entitled Critique of Practical Reason is dedicated to the ethical part of his system. In it, rather than establishing the contents of fundamental moral law, he seeks to set up the grounds. The result is his principle the "categorical imperative" and the basis for all moral action. It states:
"Act only in accord with a principle which you would at the same time will to be a universal law."
This principle led Kant to believe that we should act in accordance with our duty, not according to our feelings. He stated that the moral worth of an action should not be judged according to its consequences, but by duty. Therefore, according to Kant's ethical system, we should never tell a lie, steal or break promises regardless of what consequences this might entail. For Kant doing the right thing was not a matter of character, disposition or circumstance, but a matter of duty.
Immanuel Kant ranks with Plato and Aristotle as one of the most influential philosophers in the history of Western culture. His contributions to metaphysics, epistemology and ethics have had a profound impact on almost every philosophical movement that came after him.