The Theosophical literature offers different approaches to the constitution of human beings. One of them is in terms of the Principles, the other is through the bodies in which these principles organize themselves, and a last one is the idea of sheaths.
Before the founding of the Theosophical Society, the common notion about human beings in the West was one of a twofold nature: a body, with an inner soul or spirit. At the beginning of her Theosophical career Mme. Blavatsky explained the constitution of man as threefold, where the soul and the spirit were different principles. Master K. H. wrote to A. P. Sinnett:
[At the time] neither Christians nor Spiritualists ever thought of, let alone mentioned, more than two principles in man — body and Soul, which they called Spirit. If you had time to refer to the spiritualistic literature of that day, you would find that with the phenomenalists as with the Christians, Soul and Spirit were synonymous. It was H.P.B., who, acting under the orders of Atrya (one whom you do not know) was the first to explain in the Spiritualist the difference there was between psyche and nous, nefesh and ruach — Soul and Spirit. She had to bring the whole arsenal of proofs with her, quotations from Paul and Plato, from Plutarch and James, etc. before the Spiritualists admitted that the theosophists were right. It was then that she was ordered to write Isis — just a year after the Society had been founded. And, as there happened such a war over it, endless polemics and objections to the effect that there could not be in man two souls — we thought it was premature to give the public more than they could possibly assimilate, and before they had digested the "two souls"; — and thus the further sub-division of the trinity into 7 principles was left unmentioned in Isis. 
1- Physical: Physical body.
2- Astral: Subtle counterpart of the physical body.
3- Pranic: Vitality.
4- Kamic: Animal passions and desires.
5- Manasic: Human intelligence, Ego.
6- Buddhic: Spiritual Soul.
7- Atmic: Higher Self.
This classification is based on the form-aspect of the human being. Mme. Blavatsky did not approach this topic very much, but it was developed later by Annie Besant and C. W. Leadbeater in the Adyar tradition. The bodies were described as:
1- Dense Body: The gross part of the physical body, made of the matter we perceive through our senses.
2- Etheric Double: The subtle part of the physical body.
1- Annamayakosha: The "sheath of food", the physical body.
2- Pranamayakosha: The sheath of Prāṇa.
4- Vignanamayakosha: the sheath for higher Manas.
5- Anandamayakosha: the "sheath of bliss", for Buddhi.
In Annie Besant's view, the main differences between bodies and sheaths is that the first are organized vehicles of consciousness, while the sheaths are aggregations of matter able to communicate vibrations to consciousness, but not to be an independent vehicle of consciousness. With the process of evolution, sheaths become bodies.
Articles and pamphlets
- A Word on Man, His Nature and His Powers by Annie Besant
- The Sevenfold Division - Why Not Change the Designation? by William Q. Judge
- The Sheaths of the Soul by William Q. Judge
- Man and His Bodies by Annie Besant
- Self and It's Sheaths by Annie Besant
- The Seven Principles of Man by Annie Besant
- Vicente Hao Chin, Jr. The Mahatma Letters to A.P. Sinnett in chronological sequence No. 81 (Quezon City: Theosophical Publishing House, 1993), 246.