Kant believed himself to be creating a compromise between the empiricists & the rationalists. So the grand questions of speculative metaphysics are off limits, but the sciences are firmly grounded in laws of the mind. However, it follows from this that it's possible that there are objects of such a nature that the mind cannot think of them, & so the principle of causality, for instance, cannot be applied outside experience: hence we cannot know, for example, whether the world always existed or if it had a cause. Therefore if the mind can think only in terms of causality–which he concluded that it does–then we can know prior to experiencing them that all objects we experience must either be a cause or an effect. He concluded that all objects that the mind can think about must conform to its manner of thought. He asked if an object can be known to have certain properties prior to the experience of that object. He suggested that by understanding the sources & limits of human knowledge we can ask fruitful metaphysical questions.

Kant suggested that metaphysics can be reformed thru epistemology. Pursuing metaphysics involves asking questions about the ultimate nature of reality. Other main works of his maturity are The Critique of Practical Reason, which is about ethics, & The Critique of Judgment, about esthetics & teleology. It encompasses an attack on traditional metaphysics & epistemology, & highlights his own contribution to these areas. His most important work is The Critique of Pure Reason, an investigation of reason itself. He's regarded as one of the most influential thinkers of modern Europe & of the late Enlightenment. Immanuel Kant was an 18th-century philosopher from Königsberg, Prussia (now Kaliningrad, Russia).

Kant critique of practical reason