Mages have an innate “sixth sense” concerning all things supernatural. Their hair stands on end, goose bumps race along their arms, or a shiver runs up the spine. Regardless of the manner, their bodies react to the active presence of unseen forces (i.e., the use of a supernatural power, not simply the presence of a vampire or werewolf — unless it is using its powers). They can’t actually see or hear anything (except a mage’s nimbus when he casts spells), and they might not know at first what causes the strange reaction. To understand the feeling and its source, they can cast the Mage Sight upon themselves (or be the recipient of such a spell), and then scrutinize the scene (see below).
Mortals can purchase a similar ability, the Unseen Sense Merit (p. 110 of the World of Darkness Rulebook), but it applies to only a single type of supernatural phenomenon, such as the presence of a ghost or a vampire. For mages, this sense applies to all supernatural phenomena, alerting the willworker that the Invisible World is at hand, allowing him to cast magic to better investigate.
Mages are mortals in every way but one. They can do magic, and that makes all the difference. They can reach out to a higher world and draw down a bit of its power. Mages call this instance of borrowed might a “spell,” and all of them yearn to master even the most complex of such power grabs.
The Atlantean orders codified the metaphysics of how Supernal power interacts with the Fallen World, classifying the various phenomena as the actions of 10 elemental processes. They called these processes the “Arcana,” for their workings are not evident even to the newly Awakened. They are secrets, clues to solving the great Mysteries of the universe. It is through these secrets that spells are cast and magic is made real.