Ākāśa

Ākāśa (devanāgarī: आकाश) is a Sanskrit word meaning "space", and in Hinduism it is the first (and highest) element in creation, after which follow four more (Air, Fire, Water, and Earth).

H. P. Blavatsky defined it as follows:

Âkâsa (Sk.). The subtle, supersensuous spiritual essence which pervades all space; the primordial substance erroneously identified with Ether. But it is to Ether what Spirit is to Matter, or Âtmâ to Kâma-rûpa. It is, in fact, the Universal Space in which lies inherent the eternal Ideation of the Universe in its ever-changing aspects on the planes of matter and objectivity, and from which radiates the First Logos, or expressed thought. This is why it is stated in the Purânas that Âkâsa has but one attribute, namely sound, for sound is but the translated symbol of Logos--“Speech” in its mystic sense. In the same sacrifice (the Jyotishtoma Agnishtoma) it is called the “God Âkâsa”. In these sacrificial mysteries Âkâsa is the all-directing and omnipotent Deva who plays the part of Sadasya, the superintendent over the magical effects of the religious performance, and it had its own appointed Hotri (priest) in days of old, who took its name. The Âkâsa is the indispensable agent of every Krityâ (magical performance) religious or profane. The expression ”to stir up the Brahmâ”, means to stir up the power which lies latent at the bottom of every magical operation, Vedic sacrifices being in fact nothing if not ceremonial magic. This power is the Âkâsa--in another aspect, Kundalini--occult electricity, the alkahest of the alchemists in one sense, or the universal solvent, the same anima mundi on the higher plane as the astral light is on the lower.

Akasha is frequently related to the cosmic fifth principle:

Akâsa—of which Ether is the grossest form—the fifth universal Cosmic Principle (to which corresponds and from which proceeds human Manas.

Akasha is sometimes reffered to as primordial or cosmic substance, and is a higher aspect of the manifested cosmic matter or Prakriti:

The Tibetan esoteric Buddhist doctrine teaches that Prakriti is cosmic matter, out of which all visible forms are produced; and Akâsa that same cosmic matter—but still more imponderable, its spirit, as it were, “Prakriti” being the body or substance, and Akâsa-Sakti its soul or energy.

During pralaya Akasha as the cosmic substance is "resolved back again into the primary state of abstract potential objectivity" (mulaprakriti). When the manvantaric impulse re-awakens and Akasha is evolved, it becomes the upadhi of the cosmic ideation.

Further reading

• Ākāśa at Theosopedia