Conjuration is basically a more dark version of Spirit magic. It can allow you to reanimate the dead, as well as create demonic entities. Like the other forms of Dark Magic you don't HAVE to be an evil character to use Dark Magic. It has been practiced for centuries, but only became a mainstream form of magic a decade ago when Caer took power, as he himself uses it, as well as many of his highest wizards/sorcerors. A character using Conjuration would likely have some sort of relation to the Kingdom's army, which if I recall, Ian was an ex-soldier.