The Septenary in H.P. Blavatsky's teachings refers to the seven principles of man, In The Key to Theosophy, pp.90-93 she creates a synthesis of Eastern (Advaita Vedanta, Samkhya) and Western (Platonism, 19th century Occultism) ideas, according to which human nature consists of seven principles. These are:

• Atma - Spirit - One with the Absolute, as its radiation
• Buddhi - Spiritual Soul - The vehicle of pure universal spirit
• Manas - It has a dual nature, consisting of: a Higher Manas, the spiritual, inner, or higher Ego; and a Lower Manas, the ordinary mind which tends to join itself to the Kama (desire)
• Kama rupa - the "Desire Form", the seat of animal desires and passions; the Astral body in post-Blavatsky Theosophic literature
• Prana - The Life or Vital principle
• Linga Sharira - the Double or phantom body; the Astral body in Blavatsky Theosophic writings
• Sthula Sharira - the
  
  
  
  Gross Physical body

Despite using Sanskrit terminology, many of these concepts are quite distinct from their Indian counterparts. The Atman or Self in monistic Vedanta for example is considered the Universal Self that is the same as, and not just a "ray" of, the Absolute or Brahman.

These seven principles can be grouped into a three-fold division of Monad (transcendent Spirit, consisting of Atma and Buddhi), Ego (the higher immortal spiritual Personality, made up of the Higher Manas only) and Lower Quaternity (the mortal personality, the Lower Manas and the remaining principles). In this, the Lower Manas is a transitional princiople, the soul so to speak, whiuch can choose to to join either with the Kama (Desire) principle to form the "Kama-Manas", which becomes an "elementary" or "astral" spirit after death (equivalent perhaps to the preta or hungry ghost of Buddhism), or link with

As well as seven subtle bodies, there are also seven Kosmic Planes of existence. However, in Blavatsky's teachings, the Planes and Principles don't match up (post-Blavatskian re-interpreters like C.W. Leadbeater reinterpreted the seven principles so they equate with the seven planes; this interpretation since became standard everywhere but original or orthodox Blavatskyian Theosophy).

While undergoing some changes and modifications in the hands of later esotericists such as Leadbeater, Rudolph Steiner, and Alice Bailey, Blavatsky's description of the seven bodies or principles remained a central part of western esoteric and New Age thinking ever since.

References

• H.P. Blavatsky, The Key to Theosophy, pp.90-93