Pranayama is not, as many think, something about breath; breath indeed has very little to do with it, if anything. Breathing is only one of the many exercises through which we get to the real Pranayama. Pranayama means the control of Prâna. According to the philosophers of India, the whole universe is composed of two materials, one of which they call Âkasha. It is the omnipresent, all-penetrating existence. Everything that has form, everything that is the result of combination, is evolved out of this Akasha. It is the Akasha that becomes the air, that becomes the liquids, that becomes the solids; it is the Akasha that becomes the sun, the earth, the moon, the stars, the comets; it is the Akasha that becomes the human body, the animal body, the plants, every form that we see, everything that can be sensed, everything that exists. It cannot be perceived; it is so subtle that it is beyond all ordinary perception; it can only be seen when it has become gross, has taken form. At the beginning of creation there is only this Akasha. At the end of the cycle the solids, the liquids, and the gases all melt into the Akasha again, and the next creation similarly proceeds out of this Akasha.
By what power is this Akasha manufactured into this universe? By the power of Prana. Just as Akasha is the infinite, omnipresent material of this universe, so is this Prana the infinite, omnipresent manifesting power of this universe. At the beginning and at the end of a cycle everything becomes Akasha, and all the forces that are in the universe resolve back into the Prana; in the next cycle, out of this Prana is evolved everything that we call energy, everything that we call force. It is the Prana that is manifesting as motion; it is the Prana that is manifesting as gravitation, as magnetism. It is the Prana that is manifesting as the actions of the body, as the nerve currents, as thought force. From thought down to the lowest force, everything is but the manifestation of Prana. The sum total of all forces in the universe, mental or physical, when resolved back to their original state, is called Prana. “When there was neither aught nor naught, when darkness was covering darkness, what existed then? That Akasha existed without motion.” The physical motion of the Prana was stopped, but it existed all the same.
At the end of a cycle the energies now displayed in the universe quiet down and become potential. At the beginning of the next cycle they start up, strike upon the Akasha, and out of the Akasha evolve these various forms, and as the Akasha changes, this Prana changes also into all these manifestations of energy. The knowledge and control of this Prana is really what is meant by Pranayama.
This is a Speech of Swami Vivekananda.