Mental plane, in occult philosophy, is the plane or level of existence above the astral plane(or astral world), a realm of abstract consciousness located between the astral plane, level of concrete consciousness, and the spiritual plane, the level of primary creative being. Like all planes in occult theory, the mental is metaphorically «above» or «below» the others because they all interpret the realm of physical matter experienced by the senses.
The mental plane is a plane of meaning, pattern, and the laws of nature and mathematics; number, geometrical form, and music best communicate its nature. It resides outside of space and time. Most methods of occult meditation are attempts to raise the mind up from the concrete, quasi-sensory experiences of the astral level to the pure meanings and relationships of this mental level. A.G.H.
Greer, John Michael. The New Encyclopedia of the Occult. St. Paul. MN. Llewellyn Worldwide. 2005. p. 304