Avaridus the Philosopher was born in Mercantis; this particular fact chafes Milean pride, for the ancient Mercantine City was a great competitor of Miles in the Sword Age. However, by the time Avaridus was born the freedom of Mercantis had been captured, swallowed up, by the great imperial ambitions of the Pillar-City. Thus, it is with only a little self consciousness that Mileans can lay claim to ancient Avaridus and his well-known texts. There are many legends about him; from the myth that he was a sorcerer, to the legend that he brought in Demons from the nether world and bound them to his will. The only truths we know of Avaridus, however, is that he was born a slave in Mercantis, was trained by his master Thorios, and then purchased his own freedom at the age of thirty five. By then he had already written De Structura et Forma and was beginning his treatises on the nature of magic.
Today we're going to examine the Synthesis and how Avaridus explained the nature of the soul. This is important both for the development of philosophical thought in Arunë and also for mechanics within AD&D as they're expressed in the game.
Motion cannot begin without prior motion. Therefore, we must consider that all living things contain a manner of interior motion. This mover-within the Ancestors referred to as a soul. However, it is clear from their behavior that all things which live do not possess the same nature or number of souls. The most basic element is that of growth and change; this is the vegetative soul, which all living things possess. Most plants possess this soul alone, for they cannot move. They are confined simply to the process of breaking down food and transforming it into themselves. All souls interact with the environment thusly: they must take in, and what they take in they make into themselves. This is the process of integration and digestion.
The second form of soul is possessed by some mobile plants and all animals; this is the animalistic soul, which guides creatures to mate, to eat, and to fulfill other base urges. A limited form of cognition appears to be a symptom of this soul, but its movement in that regard is quite restricted.
The third form of soul is the rational soul, possessed by all things which can think and regard. The rational soul is the maker of thought and reason, the progenitor of that mental mental movement which leads to understanding.
These souls are not separate from the body, as the Ancients wrote. Neither are they necessarily immortal (though they may achieve this state accidentally). They are, in fact, a form of reified material that is housed in the humoral composition of the body. When the bodily humors are disordered, so too is the soul. Without the soul, the body is simply flesh without will or force. A soul without flesh would be too fragile to exist, being shredded by even the lightest breeze or the pattern of sunlight striking it. One cannot exist without the other.
This does not spell the certain extinction of the soul upon death. The spirits of Akem, the pscyhopomps, may guide the soul to the Nether World where it is then preserved and protected from such unkind forces. Or, great trauma may cause the soul lodged in a dead or dying body to form a powerful connection to this world. It must then draw energy from somewhere to maintain its cohesion, and thus we have the treacherous houseless souls we refer to as ghosts, haunts, spectres. [Editor's Note: magi studying Avaridus later deduced this "connection" to be a conduit with the Negative Material Plane, which allows the spirit to maintain cohesion outside the body also generates the "suction" effect by which the apparition may draw away fragments of the souls of the living]
The soul is separate from the function of Memory, which is a physical process that occurs within the body. It is a pattern by which the physical body is built and moved, but it is also patterned in turn by the physical nature of the body; changes to the living form may restructure the soul just as a magical transplantation of one agent-soul into another body may cause the agent-soul to lose awareness of itself and function as the natural soul of the body. Here I refer to the ancient adage of the wizard who transforms himself into a chicken and forgets he is a man.
What does this mean in context to actually playing? Not only does it bring some real Classical philosophy into the circuit of the game, it also endeavors to explain the soul as life-energy (ie, levels), the ability of the undead to drain that life-energy, and several other magical effects. It is integral to the 10th Age conception of magic as a motive force (once again, another article!) and forms the very core of thought about immortality, death, and funerary rites. The appearance of ghosts and spectres rely on the Avaridian understanding of the soul, as does their inability to form permanent new memories, leaving them to in a state of confusion about temporality.
It also separates processes of "mind" and "soul," one of which is a mechanical engine of change, the other which is more sublime and exists in what we refer to as "spirits" or reified liquid that flows through the caverns of the brain and is pumped along with the blood to all portions of the body. It informs medical practice in the setting, as well as helps explain madness and the disordered mind, which otherwise might be incomprehensible to a classical/medieval sensibility.
Beyond all that, though, it's damn fun to talk about and speculate on, and even more fun to create. I know there are those who will warn that adding extra depth to a setting can turn people off... but those are probably not the people I wanted to game with anyway.