A brief historical commentary about "BA and KA"
As has already been stated, for the Ancient Egyptians BA and KA were component elements of the human being. Later (roughly in the 4th century b.c.), as a result of an incorrect interpretation of the term, the Ancient Greeks would begin to associate BA with the soul. Although to some extent it is possible to picture it in that way, the BA is rather one of the components of the soul.
In the Old Kingdom period possession of BA and KA was an attribute of pharaohs and gods alone. This is reflected in the "Pyramid Texts". The god Ra, for example, had 14 KAs.
BA and KA were conceived as an embodiment of the power and might of the Egyptian rulers and deities. In the Middle and New Kingdoms, as is reflected in the "sarcophagus texts" and the Book of the Dead,, BA and KA were considered to be embodiments of the life-force of all people while they lived and to continue to exist after death.
According to Ancient Egyptian beliefs, the BA dwelt in the tomb together with the deceased person, performing all his or her physical functions. The KA was not only the life-force, but also a twin, an "alter-ego" inseparable from a person in both life and death.
The hierophant-priests knew rather more about these two hypostases of the human being...
BA and KA are two energy flows, two principles, opposite and unified, different and homogenous at the same time. In constant association and interaction within the person, BA and KA are the two sources of vital energy. While they are interacting, the organism's vital functions are supported and a person exists without especial problems. The merging of BA and KA, their interaction and evolution generates the AKH.
The AKH is the intermediary between God and people or a lesser deity capable of interpreting the messages of the gods. In point of fact, the AKH is something more than a person, but not, of course, a god. It is a human being with the ability to espy the future at certain moments and to predict it.