Some other important words, which recur from time to time in the Yoga-sutras, need to be understood, though there are no exact English equivalents. As they must be used to avoid clumsy circumlocutions, it is necessary to explain them. It is said: “Yoga is Samadhi.” Samadhi is a state in which the consciousness is so dissociated from the body that the latter remains insensible. It is a state of trance in which the mind is fully self-conscious, though the body is insensitive, and from which the mind returns to the body with the experiences it has had in the superphysical state, remembering them when again immersed in the physical brain. Samadhi for any one person is relative to his waking consciousness, but implies insensitiveness of the body. If an ordinary person throws himself into trance and is active on the astral plane, his Samadhi is on the astral. If his consciousness is functioning in the mental plane, Samadhi is there. The man who can so withdraw from the body as to leave it insensitive, while his mind is fully self-conscious, can practice Samadhi. The phrase “Yoga is Samadhi” covers facts of the highest significance and greatest instruction. Suppose you are only able to reach the astral world when you are asleep, your consciousness there is, as we have seen, in the Svapna state. But as you slowly unfold your powers, the astral forms begin to intrude upon your waking physical consciousness until they appear as distinctly as do physical forms, and thus become objects of your waking consciousness. The astral world then, for you, no longer belongs to the Svapna consciousness, but to the Jagrat; you have taken two worlds within the scope of your Jagrat consciousness—the physical and the astral worlds—and the mental world is in your Svapna consciousness. “Your body” is then the physical and the astral bodies taken together. As you go on, the mental plane begins similarly to intrude itself, and the physical, astral and mental all come within your waking consciousness; all these are, then, your Jagrat world. These three worlds form but one world to you; their three corresponding bodies but one body, that perceives and acts. The three bodies of the ordinary man have become one body for the yogi. If under these conditions you want to see only one world at a time, you must fix your attention on it, and thus focus it. You can, in that state of enlarged waking, concentrate your attention on the physical and see it; then the astral and mental will appear hazy. So you can focus your attention on the astral and see it; then the physical and the mental, being out of focus, will appear dim. You will easily understand this if you remember that, in this hall, I may focus my sight in the middle of the hall, when the pillars on both sides will appear indistinctly. Or I may concentrate my attention on a pillar and see it distinctly, but I then see you only vaguely at the same time. It is a change of focus, not a change of body.