Also known as Karana Sarira(causal-seed body) or, Anandamayakosha (bliss-joy sheath), Higher mind body, Ego, Causal body, Superconscious, Soul, Buddhic body, Intuitional body.
The Causal body consists of matter of the first, second and third sub-planes of the mental plane.
In ordinary people the Causal body is not yet fully active, and consequently only that matter which belongs to the third sub-plane is vivified.
It is difficult to describe a Causal body fully, because the senses belonging to the causal world are altogether different from and higher than those we employ at the physical level.
Such memory of the appearance of a Causal body, as it is possible for a clairvoyant to bring into his physical brain, represents it as an ovoid, that being, in fact, the shape of all the higher bodies, and as surrounding the physical body of the man, extending to a distance of about 18 inches from the surface of the physical body.
In the case of a primitive man, the Causal body resembles a bubble and gives the impression of being empty. It is a mere colourless film, just sufficient apparently, to hold itself together and make a reincarnating entity, but no more. Although it is filled with higher mental matter, this [body] is not yet brought into activity, and so it remains colourless and transparent.
As the man develops, this matter is gradually stirred into alertness by vibrations which reach it from the lower bodies. This comes but slowly, because the activity of man in the early stages of his evolution are not of a character to obtain expression in matter so fine as that of the Causal body. But when a man reaches a stage where he is capable either of abstract thought, or unselfish emotion, the matter of the Causal body is aroused into response.13
The vibrations thus aroused show themselves in the Causal body as colours, so that, instead of being a mere transparent bubble, it gradually becomes a sphere filled with matter of the most lovely and delicate hues, an object beautiful beyond all conception.
The student will be familiar with the meaning of the various colours, from his study of the same phenomenon in the astral [emotional] and mental bodies. Thus pale rose expresses unselfish affection; yellow indicates high intellectual power; blue betokens devotion; sympathy is expressed by green; and luminous lilac-blue typifies the higher spirituality. These same colours in the denser bodies are, of course, far less delicate and also less living.
Although in the course of his evolution in the lower worlds, a man often introduces into his vehicles qualities which are undesirable, and entirely inappropriate for his life as an Ego - such for example, as pride, irritability, sensuality - yet none of these can be expressed in the Causal body.
Each section of the astral body acts strongly upon matter of the corresponding mental sub-plane. Hence, as the coarser vibrations of the astral body are expressed only in the lower  sub-planes of the astral world, they will affect the Mental body only, not the Causal body.
The Causal body, therefore, is affected only by the three higher portions of the astral body, and the vibrations in those portions represent only good qualities.
The practical effect of this is that the man can build, into his Ego, that is, into his true self, nothing but good qualities. The evil qualities which he develops are, from the point of view of the Ego, only transitory, and must be thrown aside as the man advances, because he no longer has within him matter which can express them.13
It might perhaps have been thought that the causal body of a primitive man would be very small at first; but this is not the case; his causal body is the same size as any other; it does at a later stage increase in size, but not until it has first been vivified and filled with active matter.
In the case of an average man, there is a distinct increase in the content of the great ovoid film. A certain amount of exceedingly delicate and ethereal colour now exists within it, though it is still less than half filled. Something of the higher intellect is visible, and something of the power of devotion and unselfish love. There is also a faint tint of that exceedingly delicate violet which indicates the capacity of love and devotion turned towards the highest ideal, and also a faint hint of the clear green of sympathy and compassion.
As soon as the man begins to develop in spirituality, or even higher intellect, a change takes place. The real individual then begins to have a persisting character of his own, apart from that moulded in each of his personalities in turn by training, and by surrounding circumstances. this character shows itself in the size, colour, luminosity, and definiteness of the causal body, just as that of the personality shows itself in the mental body, except that the higher vehicle is naturally subtler and more beautiful.
In the case of the spiritually developed man, an enormous change is noticed. the glorious iridescent film is now completely filled with the most lovely colours, typifying the higher forms of love, devotion and sympathy, aided by an intellect refined and spiritualised, and by aspirations reaching ever towards the divine. Some of these colours have no place in the physical spectrum.13
The student will scarcely need to be told that all description of buddhic consciousness is necessarily and essentially defective. It is impossible in physical words to give more than the merest hint of what the higher consciousness is, for the physical brain is incapable of grasping the reality.
It is difficult enough to form a conception even of astral plane phenomena, there being four dimensions in the astral world. In the buddhic world there are no less than six, so that the difficulties are enormously enhanced.
There is an ingenious diagram (for which the [author] is indebted to the unknown designer) reproduced below, which illustrates graphically the fundamental difference between the buddhic plane and all the planes below it.
The diagram [Unity in Diversity] is seen to consist of a number of spikes or spokes which overlap at a certain point. That point of overlap is the beginning of the buddhic plane. The tips of the spokes represent the physical consciousness of men: they are separate and distinct from one another. Passing up the spokes towards the centre, we see that the astral consciousness is a little wider, so that the consciousness of separate men approach a little nearer to one another. The lower mental consciousnesses aproach still more nearly to one another, whilst the higher mental consciousnesses, at their very highest level, meet at the point where the buddhic consciousness commences.
It will now be seen that the buddhic consciousness of each individual and separate "man," overlaps that of the other separate consciousnesses on either side of him. To the left is a graphic illustration of the "overlapping" aspect of buddhic consciousness, where a sense of union with others is experienced.
As the consciousness rises still further up into the higher plane, it will be seen that it overlaps those on either side of it more and more, until eventually, when the "centre" is reached, there is practically a complete merging of consciousness. Nevertheless each separate spoke still exists and has its own individual direction and outlook. Looking out towards the lower worlds, each consciousness looks in a different direction: it is an aspect of the one central consciousness. Looking inwards, on the other hand, these diverging directions all meet together, and become one with one another.
The sense of union is characteristic of the buddhic plane. On this plane all limitations begin to fall away, and the consciousness of man expands until he realises, no longer in theory only, that the consciousness of his fellows is included within his own, and he feels and knows and experiences, with an absolute perfection of sympathy, all that is in them, because it is in reality a part of himself.
On this plane a man knows, not by mere intellectual appreciation, but by definite experience, the fact that humanity is a brotherhood, because of the spiritual unity which underlies it all, though he is still himself, and his consciousness is his own.13
High unselfish affection and devotion belong to the highest (atomic) astral sub-plane, and these reflect themselves in the corresponding matter of the mental plane. They thus touch the causal (higher mental) body, not the lower mental. This is an important point of which the student should take especial note.
The Ego, who resides on the higher mental plane, is thus affected by only unselfish thoughts. Lower thoughts affect, not the Ego, but the permanent atoms. [this subject is not addressed here on this website - see the referenced book].
Consequently, in the Causal body there would be gaps, not bad colours, corresponding to the lower feelings and thoughts.
Selfishness, for example would show itself as the absence of affection or sympathy: as soon as selfishness is replaced by its opposite, the gap in the Causal body would be filled up.
An intensification of the coarse colours of the astral body representing base emotions, whilst finding no direct expression in the causal body, nevertheless tends somewhat to dim