It is not proposed to deal in detail in this article with the vexed question of the nomenclature of the Planes in Nature, but mention must be made of certain alternative systems that have been used. The system adopted by later writers within Theosophical Society (TS) was suggested by Annie Besant and Charles W. Leadbeater and categorize the mental plane as the higher or causal and the lower mental plane; these are “flanked” by the astral below and the buddhic above.

The mental plane is plane on which the processes of thought operate. The term “plane” is used in theosophy in a special or technical sense and not in its dictionary meaning of level or flat. “Plane” is defined by Helena P. Blavatsky in her The Theosophical Glossary, “The term denotes the range or extent of some states of consciousness. . . .” Perhaps the term “Plane” is not the best choice as it tends to imply a stacking of planes one above the other whereas in fact the planes interpenetrate each other. The mental plane has been described as a reflection of the Universal Mind of Nature, the term “Nature” as used here denotes the manifested Cosmos. This Universal or “Great Mind” is variously called Mahat, or the Third Logos, or the Divine Creative Intelligence.

What has been termed the “elemental essence” that makes up the mental plane is formed by the MONAD in one of the stages of its descent into matter, immediately before its entrance into the astral plane. Here, on the four lower sub-divisions, we find the Second Elemental Kingdom; the First Elemental Kingdom occupies the three higher “levels.” The Monad has been described as eternal, unitary, individual, life-center, consciousness center, ageless, unborn and undying. Strictly speaking, the Monad does not “descend” through the planes into matter, but sends forth a “ray” which exudes the “matter” of its various vehicles.

The mental plane is divided broadly into two regions, the upper or CAUSAL and the lower. These are related respectively to abstract and to concrete thought and these are sub-divided into a total of seven sub-planes. The mental plane lies next to the astral plane and is distinct from it due to the degree of subtlety of the constituent matter. The seven sub-planes of the mental plane differ from each other not only in respect of the “fineness” of the mental matter that constitutes them, but in the degree of responsiveness of this matter. This is illustrated by the terms used to distinguish between the lower four called “with form” or in Sanskrit rūpa and the upper three called “formless” or arūpa. These regions are related, as far as consciousness and activity are concerned, to the divisions or attributes of the human mind. On the lower four “levels” of this plane every thought in the human mind gives rise to some sort of form which might be either very clear and well-defined or rather more vague and ill-defined, with an infinite degree of variation between these extremes; it may be fleeting or persistent, depending on the intensity and duration of the thought. The “higher” three levels are the realms of abstract thought and are difficult to describe in concrete terms. The function of symbols might perhaps serve to throw some light on the matter. A symbol may be illustrated by such concrete items as the Egyptian ankh or the Star of David; the inspiration for these tangible forms might be said to arise from sources on the higher plane, but they take on concrete form at the physical level. Once in existence these symbols reflect their archetypal origins in their universality of meaning that transcends language. According to some theosophical writers the mental plane is not solely associated with the physical planet Earth as we now know it, but with the chain of globes. The presiding deity of the Solar System, the Logos, manifests the system on more than one level. Thus we note the existence of seven levels on which “globes,” comprising a chain, exist. The mental plane is associated, so it is said, with the globes A and G. Each physical planet in our system is said to have associated with it planes such as astral and mental.

Thought-forms are an important subject of the mental plane discussion; each thought gives rise to its corresponding entity on that plane. Clear and long maintained thought generates a clear and well-defined form which might persist for an indefinite length of time. Such thought-forms are described as radiant and brilliantly colored in appearance.

Thought-forms generated by dull or badly trained minds are vague in outline and transient. The subject of thought-forms has received detailed treatment in a book by that title by Annie Besant and Charles Leadbeater. This book has been credited with exerting strong influence on the arts during the early twentieth century, particularly on the impressionists.

A vast number of “Intelligences” exist on the upper and lower regions of the mental plane whose bodies are composed of the elemental essence. These entities have been called Shining Ones (Sk. Devas) and they are said to guide the processes of Nature at the physical level. They are beings of supernal intelligence, transcendent powers and splendid aspect. They work through a myriad of ELEMENTALS each of whom is dedicated to some special work. The human relationship to the Mental Plane is very close since that part of the human subtle constitution that is a Mental Body lies, in degree of subtlety, between the astral body and the causal. Since the mental body is composed of material derived from the Mental Plane it follows that much of the thought processes of the human affects the Mental Plane (see MENTAL BODY).

Certain highly developed individuals, such as chelas of the Mahātmas, are able to do conscious work on the Mental Plane in their Mental Bodies known in Sanskrit as Māyāvi Rūpa, or illusory body, when independently functioning in the mental world. While asleep such individuals are able to help others by impressing on their minds noble thoughts or high ideals. Communication on the Mental Plane is almost instantaneous and above all relatively undistorted. Such an ability is not, of course, confined to chelas but may be possessed by any individual who has undergone the requisite training in such a discipline as, say, Rāja Yoga. According to Annie Besant, the Egos of the Masters of the Wisdom and other Initiates dwell on the third level of the upper region and they have a preponderance of the matter of the mental plane in their bodies (The Ancient Wisdom, p. 119).

P.S.H.