The basic idea behind the Archmage is a ranged (spell) DPS/Healing hybrid, viable for both PvE and PvP.

Unlike other casters, the Archmage does not begin with a full mana pool, but instead earns mana through casting (much like a rogue).

The class has a number of basic spells and abilities (some designed for healing and others for dealing damage) that can be cast for no cost, but are much less effective (but not completely worthless).

By using these abilities their mana pool begins to build, opening up more effective spells and heals.

While it would be possible to only heal (Priest), or DPS (Mage) - doing so would be much less effective.

A good Archmage would need to balance both dealing damage and healing those around them in order to do both to their full effect.

The three talent trees would allow players to improve their DPS abilities (PvP or group/raid PvE DPS), their healing (group/raid PvE) or survivability (solo PvE) - but even with talents fully spent in one talent tree both healing and DPS would be required to fully get the most from the class.