Let us take it in detail. Four states of consciousness are spoken of amongst us. “Waking” consciousness or Jagrat; the “dream” consciousness, or Svapna; the “deep sleep” consciousness, or Sushupti; and the state beyond that, called Turiya (It is impossible to avoid the use of these technical terms, even in an introduction to Yoga. There are no exact English equivalents, and they are no more troublesome to learn than any other technical psychological terms.) How are those related to the body?
Jagrat is the ordinary waking consciousness, that you and I are using at the present time. If our consciousness works in the subtle, or astral, body, and is able to impress its experiences upon the brain, it is called Svapna, or in English, dream consciousness; it is more vivid and real than the Jagrat state. When working in the subtler form — the mental body — it is not able to impress its experiences on the brain, it is called Sushupti or deep sleep consciousness; then the mind is working on its own contents, not on outer objects. But if it has so far separated itself from connection with the brain, that it cannot be readily recalled by outer means, then it is, called Turiya, a lofty state of trance. These four states, when correlated to the four planes, represent a much unfolded consciousness. Jagrat is related to the physical; Svapna to the astral; Sushupti to the mental; and Turiya to the buddhic. When passing from one world to another, we should use these words to designate the consciousness working under the conditions of each world. But the same words are repeated in the books of Yoga with a different context. There the difficulty occurs, if we have not learned their relative nature. Svapna is not the same for all, nor is Sushupti the same for everyone.
Above all, the word samadhi, to be explained in a moment, is used in different ways and in different senses. How then are we to find our way in this apparent tangle? By knowing the state which is the starting-point, and then the sequence will always be the same. All of you are familiar with the waking consciousness in the physical body. You can find four states even in that, if you analyse it, and a similar sequence of the states of the mind is found on every plane.
How to distinguish them, then? Let us take the waking consciousness, and try to see the four states in that. Suppose I take up a book and read it. I read the words; my eyes arc related to the outer physical consciousness. That is the Jagrat state. I go behind the words to the meaning of the words. I have passed from the waking state of the physical plane into the Svapna state of waking consciousness, that sees through the outer form, seeking the inner life. I pass from this to the mind of the writer; here the mind touches the mind; it is the waking consciousness in its Sushupti state. If I pass from this contact and enter the very mind of the writer, and live in that man's mind, then I have reached the Turiya state of the waking consciousness.
Take another illustration. I look at any watch; I am in Jagrat. I close my eyes and make an image of the watch; I am in Svapna. I call together many ideas of many watches, and reach the ideal watch; I am in Sushupti. I pass to the ideal of time in the abstract; I am in Turiya. But all these are stages in the physical plane consciousness; I have not left the body.
In this way, you can make states of mind intelligible and real, instead of mere words.