奥义书——吠陀传统的哲学核心，阐明梵、真我、知识、行动与解脱的本质。十部主要奥义书，另加精选的毗湿奴派小奥义书。
On the "swan" — the soul, which flies between breath and thought — and on the inner sound heard in silence. The book is short and almost entirely about hearing: ten sounds, from a buzzing to a thunder, and what to do with the last of them.