The Four Dhyanas are higher states or realms of consciousness (levels of Samadhi–see Samadhi) reached in two ways: a) temporarily, through correct meditation, and b) on a lifetime basis through rebirth as a God in the Dhyana-heavens (see Gods).
One enters the first Dhyana by abandoning vitArka (“examination”), which refers to coarse polluted thinking. One is thus separated from one's afflictions. In the first Dhyana a more subtle kind of polluted thinking called vicara (“investigation”) still remains, as do priti (“bliss”) and sukha (“happiness”). Priti is a type of blissful light ease associated with the body, and sukha is a more subtle and pure happiness or joy. When one enters the second Dhyana vicara is eliminated, and a finer experience of bliss from one's meditational state remains. In the third Dhyana priti is eliminated, so that only the pure happiness of sukha remains. And in the fourth Dhyana sukha, a very subtle cognitive function of the mind, is also eliminated to lead to an even purer state of mind.
“Dhyana is a Sanskrit word meaning 'meditation', . . . the purifying and quieting of cognitive considerations. . . . “When you reach the first Dhyana, your pulse stops, and you can sit for seven days at a time without getting up from your seat, eating or drinking. . . . There is no happier experience in the world–it is the happiness of the heavens, not that of the human realm. When you reach the second Dhyana, you can sit for Forty-nine days at a time without getting up, eating or drinking. While in that Samadhi , the joy is far Greater than that of the first Dhyana. When you reach the third Dhyana, you have no thought, and can sit for Three years at a sitting. And so you claim that you've . . . become enlightened? Can you even sit for Three days at a time? . . . When one reaches the state of the fourth Dhyana, one can sit for nine years without getting up, eating or drinking. At that time, one doesn't merely stop having thoughts; the thought process stops altogether, and one's consciousness is unmoving. Although without movement, consciousness still exists. . . .” (FAS-PII]](1) 35-39)
“The second Dhyana is called the ground of bliss born of Samadhi. . . . In the second Dhyana, one's breath stops. There is no detectible breathing in and out, but at that time an inner breathing takes over.
“The third Dhyana is the ground of the wonderful happiness of being Apart from bliss. One renounces the Dhyana-bliss as food and the happiness of the Dharma that occurs in initial Samadhi. One goes beyond that kind of happiness and reaches a sense of wonderful joy. It is something that one has never known before, that is inexpressible in its subtlety, and that is inconceivable.
At the point when not one thought arises, the entire substance and Great function (of your Buddha Nature) are in evidence. But once your six organs suddenly move, then it is obs[[cured. It just takes a slight movement by the eyes, ears, nose, tongue, body, or mind to cause this to happen. Then one is covered over by the Clouds of the Five Skandhas.
“The fourth Dhyana is called the ground of the clear purity of Casting away thought. In the third Dhyana thoughts were stopped–held at bay–but they still had not been renounced altogether. In the heavens of the fourth Dhyana, not only are thoughts stopped, they are done away with completely. There basically are no more cognitive considerations. This state is extremely pure, subtly wonderful, and particularly blissful.
“However, reaching the fourth Dhyana is simply a preliminary, expedient state of meditational inquiry reached by beginners. Having reached this state is of no use at all in itself. It is not Certification of Sagehood. You shouldn't make the mistake of thinking that reaching these four levels makes you somehow very special. . . . You've only experienced a bit of the flavor of Chan.” (LY II 75-76)