“Enq: But why should not man be represented by two “principles” or two aspects, rather?
Theo: Every man has these two principles in him, one more active than the other, and in rare cases, one of these is entirely stunted in its growth, so to say, or paralyzed by the strength and predominance of the other aspect, in whatever direction.
These, then, are what we call the two principles or aspects of Manas, the higher and the lower; the former, the higher Manas, or the thinking, conscious Ego gravitating toward the spiritual Soul (Buddhi); and the latter, or its instinctual principle, attracted to Kama, the seat of animal desires and passions in man.
Thus, we have four “principles” justified; the last three being (1) the “Double”, which we have agreed to call Protean, or Plastic Soul; the vehicle of (2) the life principle; and (3) the physical body. Of course no physiologist or biologist will accept these principles, nor can he make head or tail of them.
And this is why, perhaps, none of them understand to this day either functions of the spleen, the physical vehicle of the Protean Double, or those of a certain organ on the right side of man, the seat of the above-mentioned desires, nor yet does he know anything of the pineal gland, which he describes as a horny gland with a little sand in it, which gland is in truth the very seat of the highest and divinest consciousness in man, his omniscient, spiritual and all-embracing mind.
And this shows to you still more plainly that we have neither invented these seven principles, nor are they new in the world of philosophy, as we can easily prove.”
H. P. Blavatsky