"Critique of Pure Reason" is a philosophical work by Immanuel Kant, published in 1781. It explores the relationship between human experience and knowledge, arguing that our understanding of the world is shaped by both sensory experience and innate concepts. Kant distinguishes between a priori knowledge, which is independent of experience, and a posteriori knowledge, which is derived from experience. The book introduces the idea of the "transcendental" as a way to understand how we perceive reality. Kant examines the limits of human reason and argues that while we can know phenomena (the world as we experience it), the noumena (the world as it is in itself) remains ultimately inaccessible to us.