Buddhist philosophy refers to the philosophical investigations and systems of inquiry that developed among various Buddhist schools in India following the death of the Buddha and later spread throughout Asia. Buddhism's main concern has always been freedom from dukkha (unease), and the path to that ultimate freedom consists in ethical action (karma), meditation and in understanding the nature of reality (prajña). Indian Buddhists sought this understanding not just from the revealed teachings of the Buddha, but through philosophical analysis and rational deliberation. Buddhist thinkers in India and subsequently in East Asia have covered topics as varied as phenomenology, ethics, ontology, epistemology, logic and philosophy of time in their analysis of this path.