A kosha (also kosa; Sanskrit कोश, IAST: ), usually rendered "sheath", is a covering of the Atman, or Self according to Vedantic philosophy. There are five koshas (Panchakoshas; ; the five sheaths), and they are often visualised as the layers of an onion in the subtle body. The Tvam ("Thou") padartha of the Mahavakya Tat Tvam Asi is determined by the analysis of Panchakoshas that are not the atman. Panchakoshas are discussed in the Brahmanandavalli Chapter of Taittiriya Upanishad which is a part of the Taittiriya Samhita of the Krishna Yajur Veda and in which particular chapter is discussed ways and means to achieve Brahman. It gives a detailed description of the dimensions of human personality or the dimensions of the Self. Atman The Sruti declares that human birth, by divine grace, is meant to strive to know and understand the atman. The knowledge and understanding of the atman invariably results in Jiwanmukti i.e. Moksha or "Spiritual liberation". Spiritual Liberation is of the nature of bliss in which there is complete negation of all sorrow, it does not arise by mere study of sastras, sacrifice to gods, performance of karmas and meditation on the divinities, these acts do not result in the knowledge of the unity of atman. Atman is Brahman who is of the nature of satyam, jnanam and anantam, and the knower of Brahman becomes Brahman. Knowledge is gained after renouncing attachment to all sense-objects and all actions, for one's body, that harbours the mind that makes for bondage and is not the atman. The Atman is the substratum of the consciousness of "I". Anatman Anatman means not-self or non-self. Anatman is everything that is not Atman. All objects of consciousness are called Anatman, including the mind and the ego. The samsara is the vast turbulent ocean which is the embodiment of avidya and its effects that cannot be crossed without the aid of perfect wisdom; the samsara is the anatman. By non-realisation of the true nature of the atman, the atman is mistaken as the karana sarira ("causal body"), suksma sarira ("subtle body") and sthula sarira ("gross body") which bodies constitute the anatman. For a person who is unaware of the atman there is no other go except to do karmas intended for purification of the mind. Origins The five sheaths summarised with the term Panchakosha are described in the Taittiriya Upanishad (2.1-5). From gross to fine