Transcendental Idealism posits that the mind plays an active role in shaping our experience of reality. According to Kantianism, our knowledge is not a passive reflection of an objective external world, but rather the result of the interaction between sensory experience and the mind's inherent structures and concepts.
Kant distinguishes between the "phenomenal" and the "noumenal" realms. The phenomenal realm refers to the world of appearances that we perceive and interact with through our senses. This world is structured and organized by the mind through its innate categories of understanding, such as space, time, causality, and substance. These categories are not derived from experience but are inherent in the human mind and serve as the framework for organizing and interpreting sensory data.