PERHAPS some additional light may be thrown upon this subject supposed to be so complex if we reason backward instead of forward, inquiring what the constitution of man would seem of necessity to be, and not merely investigating what it in fact is. And this may be done by thought upon the "final cause" of his evolution.
A final cause is the end or object of an action, that for the sake of which anything is done, this purposeful aim having therefore the force of causality. The final cause of a man's evolution is the production of a being perfect in knowledge and experience. Hence, very evidently, the knowledge and experience must be in every quarter, on every plane, through every function. Now there are three ways whereby knowledge is acquired, — sensation, perception, and intuition. Sensation is the way through use of the bodily organs, as when information of the nature of a table or chair is gained by touch and sight. Perception is the way through use of the mental and reasoning faculty, as when information of facts in geometry is gained by reflection on the necessary properties of figures. Diagrams may aid to comprehension, but the fact that the three angles of a triangle are equal to two right angles exists independently of any drawing which may be used to illustrate it. Intuition is the way through use of the higher, super-sensuous faculties, by which supersensuous truth is directly, without the medium of ratiocination or inference, seized at once.
If we can imagine a purely spiritual, unembodied being, such a being as is suggested by the word "angel", it is clear that his only avenue to truth would be through intuition. Without physical organs, and raised above the plane whereon argument and induction range, intuition would be his one resource. Of life and movement in his own sphere, of methods of communication in thought and sympathy, he would have copious knowledge. But there it would stop. Of the gradual processes of reflection and reason used in lower fields, much more of such experimental tuition as comes through bodily life with bodily organs, not the remotest conception would be possible. Not only would matter, with all its sensations and restrictions, be foreign to him, but he would be a stranger to such emotions as result from the relations and casualties of social existence on earth, — sorrow, pity, sympathy, self-forgetfulness, self-sacrifice. That is to say, he would be ignorant of a vast range of instructive experiences, and incapable of a large group of refining emotions.
If such a being is to supplement his apprehension of the cosmos by an understanding of that part of it which has consolidated into gross matter, he must incarnate, must dwell in and learn of the section he does not know. He has within him a spark from the Divine Essence, and that is enshrined in a spiritual nature removed the one step from pure Divinity which makes possible an individuality distinct from it. To these he is to add a physical body.
But put a spiritual being into such a body, and no junction results. There is no connecting tie, nothing to bridge over the chasm between two entirely unlike natures. There must be something to enable the spiritual to act upon the physical, and the physical to send messages to the spiritual. Mind does this. On its higher side it reaches up to and affiliates with spirit; on its lower it grasps and influences subtile matter. Though these opposite functions constitute really two entities, they are so interlaced that they blend into each other and permit the passage of thought and will. Thus we have five principles.
Still there is a gap. Intangible mind cannot directly act on gross matter, being still too ethereal for immediate influence. A transmissive medium between mind and flesh is as needful as one between spirit and matter. There is required a body so constituted as to touch at the same time both mind and flesh, supplying a connection for vibrating influences. The astral body does this. The real seat of the organs manifested in those of our five physical senses, it can catch from the physique the sensations they receive and then transmit them to the intelligence above. For it is this astral body which is as to this plane the real seer, hearer, taster, toucher, smeller, and which mediates between gross flesh and subtile mind. And thus we have six principles.
But what would an organism of flesh and bones be without the vitalizing force to conserve and move it? Simply an inanimate mass. So to energize it for action there must be a pervading life, a life of respiration and digestion and circulation and reproduction. The everywhere-distributed vivifying element in Nature supplies this. Vibrating in each atom it thrills through the system and makes it a part of the great whole, transforming a mere apparatus into a living, functioning, active animal. And thus we have seven principles.
If, then, a pure spirit is to incarnate for experiential knowledge, the necessities of the case appear to exact precisely that sevenfold nature which Theosophy asserts of man. A priori considerations conduct to the conclusion otherwise demonstrable as fact.
On the supposition that there are these various elements in man, what would naturally be their behavior when the life-principle is withdrawn from the physical body at what we call "death"? This leaves as the enclosure of the five remaining principles an inanimate form, insusceptible of influence to or from, and already beginning to disintegrate. This not only dispenses from their longer union for experiential purposes, but directly prompts to a severance. For the spirit enshrined in a spiritual nature no longer needs the link connecting it with a body now worthless, and presumably would retire till ready for another incarnation. But its close union with the Higher Mind has suffused the latter with something of its own pure nature, imparting to it an immortal life. On the other hand, the close union of the Lower Mind with the physical body through the astral has tainted it with the corruption which bespeaks mortality. So the interfacings naturally drop apart, the mortal separates from the immortal. The three higher principles pass on.
Why should the Lower Mind and the astral form cohere? The latter is no longer a vehicle for transmission of sensation upwards or volition downwards. It, too, with the body, has lost its vitality by the withdrawal of the Life-principle, and must drop away from the Lower Mind for the same reason that the Lower has dropped from the Higher Mind and both from the body itself. The second principle having departed, the first, third, and fourth fall separately into gradual dissolution, while the fifth, sixth, and seventh, of undying nature, can have no further touch with what are soon to end.
And here again, what would antecedently seem probable is declared a fact by the teachings of Theosophy. Those who know affirm the conclusions of those who think. The opposite processes of reason and revelation coincide in the result of vindicating the Seven-fold Principle in Man, both as to the necessity of his construction and the method of his dissolution.
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