Transcendental Idealism is a philosophical theory developed by Immanuel Kant in the late 18th century. It posits that our understanding of the world is shaped by the way our mind structures experiences. According to this view, we can never know things as they are in themselves, but only as they appear to us through our senses and cognitive faculties. Kant argued that certain concepts, like space and time, are not inherent properties of the external world but rather frameworks through which we perceive reality. This means that while we can gain knowledge about phenomena, the noumena, or things-in-themselves, remain ultimately inaccessible to human understanding.