Some of the terms used in Yoga are necessarily to be known. For Yoga takes man for a special purpose and studies him for a special end and, therefore, only troubles itself about two great facts regarding man, mind and body. First, he is a unit, a unit of consciousness. That is a point to be definitely grasped. There is only one of him in each set of envelopes, and sometimes the Theosophist has to revise his ideas about man when he begins this practical line. Theosophy quite usefully and rightly, for the understanding of the human constitution, divides man into many parts and pieces. We talk of physical, astral, mental, etc. Or we talk about Sthula-sarira, Sukshma-sarira, Karana-sarira, and so on. Sometimes we divide man into Anna-maya-kosa, Prana-maya-kosa, Mano-maya-kosa, etc. We divide man into so many pieces in order to study him thoroughly, that we can hardly find the man because of the pieces. This is, so to say, for the study of human anatomy and physiology. But Yoga is practical and psychological. I am not complaining of the various sub-divisions of other systems. They are necessary for the purpose of those systems. But Yoga, for its practical purposes, considers man simply as a duality—Mind and Body, a Unit of consciousness in a set of envelopes. This is not the duality of the Self and the Not-Self. For in Yoga, “Self” includes consciousness plus such matter as it cannot distinguish from itself, and Not-Self is only the matter it can put aside. Man is not pure Self, pure consciousness, Samvid. That is an abstraction. In the concrete universe there are always the Self and His sheaths, however tenuous the latter may be, so that a unit of consciousness is inseparable from matter, and a Jivatma, or Monad, is invariably consciousness plus matter. In order that this may come out clearly, two terms are used in Yoga as constituting man—Prana and Pradhana, life-breath and matter. Prana is not only the life-breath of the body, but the totality of the life forces of the universe or, in other words, the life-side of the universe. “I am Prana,” says Indra. Prana here means the totality of the life-forces. They are taken as consciousness, mind. Pradhana is the term used for matter. Body, or the opposite of mind, means for the yogi in practice so much of the appropriated matter of the outer world as he is able to put away from himself, to distinguish from his own consciousness.