At it’s core, Magic is altering the properties of something in Eidos without using it’s material form as the medium for change. Take a tennis ball. You could accelerate it by hitting it with a tennis racket. You could also accelerate it by adding velocity to it’s Form in Eidos; since Eidos directly impacts how the material world works, the ball would sudden accelerate to the modified velocity.
There are three main guidelines:
- First, changes that do not make sense by material physics cease when the interference of magic ceases. The ball will not continue to defy friction and gravity, nor will it defy conservation of motion; if the ball is in the atmosphere, it will slow down and eventually stop, just as if you’d hit the ball with a racket. However, if you can make a ‘stable’ change, there will be nothing to revert – for example if you destroy a rock to pebbles, the pebbles will not reform into the rock, as pebbles are consistent within the system of reality.
- Second, while altering Eidos ignores conservation of mass and energy (just as cheating in a video game would bypass the physics engine); it is not an unlimited power. The greater the change violates the rules, the harder it is to make.
- Third, changing Eidos requires Mana (the IDS refers to Mana as ‘psionic particles’). The nature of this energy is poorly understood, and directly interacting with it is challenging.
The greatest problem with Eidos – and for that matter mana – is they, by definition, are not part of the material world; there is no direct way to interact with them, and thus the actual mechanics of how a mage works magic is unknown – the conceptual leap from understanding that Eidos exists to understanding how to change it is what makes someone a ‘Mage’