The Circle of Powers
The powers of magic are divided into what is commonly known as the "Circle
of Powers". This is actually just a framework for the understanding of
magic used by mages but works well as a teaching tool for novice mages
and to explain magic to non-mages.
The Circle Explained 
There are four fundamental forms of magic (known as the primary forms):
Earth, Fire, Air, and Water. These are graphically shown as being arrayed
around a circle with the opposing forms on opposite sides of the circle
(Earth/Air, Fire/Water). Each form has one opposing form and two forms
that are neutral to it.
There is a different kind of Magery for each primary form and thus there
are four kinds of mages. All the colleges of magic derive from one or two
of the primary forms. [There are no other forms of magery such as "Sun
Magery" nor is there any "generic" Magical Aptitude.] The colleges of magic
have one of six relationships with each of the primary forms.
The following assumes that we are observing the circle from the perspective
of an Earth mage.
-
Aligned colleges are those that derive their power exclusively from the
primary form. For example, the Earth, Plant, and Food colleges derive their
power solely from the primary form Earth. Mages casting spells aligned
to their form of Magery gain a significant skill boost [+2 skill per level
of Magery].
-
Allied colleges are those that derive their power from the primary form
and from a neutral form. For example, the Animal and Body Control colleges
derive their power from both Earth and Water. Mages casting spells allied
to their form of Magery gain a skill boost [+1 skill per level of Magery].
-
Neutral colleges are those that derive their power exclusively from a neutral
form. For example, the Water and Healing colleges derive their power solely
from the primary form Water (neutral to Earth). Mages casting spells neutral
to their form of Magery gain no skill boost nor can they learn spells in
those colleges that require Magery.
-
Adverse colleges are those that derive their power from the opposed form
and from a neutral form. For example, the Movement and Communication &
Empathy colleges derive their power from both Air (opposed to Earth) and
Water (neutral to Earth). Mages casting spells adverse to their form of
Magery have a skill penalty [-1 skill per level of Magery] and can not
learn spells in those colleges that require Magery.
-
Opposed colleges are those that derive their power exclusively from the
opposed form. For example, the colleges Air and Sound derive their power
solely from the primary form Air (opposed to Earth). Mages casting spells
opposed to their form of Magery have a significant skill penalty [-2 skill
per level of Magery] and can not learn spells in those colleges that require
Magery.
-
Nonaligned colleges are those that derive their power from all primary
forms equally. The three nonaligned colleges are Meta, Knowledge, and Enchantment.
Mages casting nonaligned spells gain a skill boost [+1 skill per level
of Magery].
These relationships are shown graphically in the "Relationships"
figure. [Note that a skill penalty does not preclude learning spells in
a college (excepting those that require Magery). Such spells may only be
cast in areas with high mana as for non-mages. The total skill bonus in
a college is what is used when testing against "Magery X" prerequisites,
e.g., an Earth mage with Earth Magery 1 could learn spells in the Earth
and Plant colleges that had "Magery 2" as a prerequisite.]
The Colleges
The colleges are arrayed around the circle as in the following graphic.
The Earth primary form is at the top, Fire is to the right, Air is at the
bottom, and Water is to the left.