Potential mages comprise 4% of the sapient population of Elcenia, but they have no special powers until activated. Magery consists of control over a single classical element (air, earth, fire or water) but is only potential until the person who can become a mage would otherwise die in a specific situation related to the element. (Traditionally, these ways are falling from heights, being crushed by landslides or cave-ins, burning, and drowning, but other methods are possible.)
There are spells available to determine whether someone has mage potential and, if so, which element it applies to, but (except for air mages, who are caught by the air before hitting bottom after a fall), the activation process is just as painful as it would be absent mage potential. (Taking painkillers beforehand is possible but does not typically eliminate all of the pain.) Therefore, many potential mages never choose to activate, although accidental activations occasionally happen, and activated air mages are more common than the other three types even though the potentials are equally common.
Mages (and anything they're wearing or carrying, up to 15% of their own bodyweight) can "merge" with their element, traveling through it in any direction without disturbing it. Air mages use this ability to fly. Fire mages, but not others, can conjure their elements from thin air. All mages must spend a majority of their time in contact with at least a small amount of their element or become sick.