Compelling spells nudge a preferred but possible outcome into reality. A coin toss can be made to come up tails (Fate), a bored worker can be made to take that coffee break now (Mind), or a spirit can be forced to avoid its bane (Spirit).
Making the coin hover and spin in mid-air, making the worker walk into her boss’s office and quit, or making the spirit ignore its favorited prey are beyond the bounds of a Compelling spell.
In Game:
Overall, spells of the Practice of Compelling are the most surreptitious of the magics used to directly affect the world, interacting with its people, places and things through the use of the Arcana alone. Compelling spells might grant a bonus to the mage properly exploiting the spell’s results, but such magics don’t usually create the circumstances under which the bonus would come into play. Think of it more like making temporary magical equipment: the willworker still has to set up the situation so as to make use of the bonus.
Even as mages grow in power and experience, the Practice of Compelling remains an eminently useful one. You never know when you’ll need to adjust circumstances just a little bit. Even the most skillful master can find a reason to change this detail or that one every so often. Compelling magics won’t reshape the Fallen World, and they usually aren’t sufficient, in and of themselves, to make the difference at those crucial times, but they can push things in the right direction, and help an insightful willworker to make those changes for herself, whether through other, more powerful magics, or even through fully mundane capabilities.
In Story:
Some Free Council mentors jokingly refer to this as the “Practice of Suggesting,” as the mage isn’t so much exerting any kind of control over the phenomenon in question as gently nudging it in small ways. Still, Compelling effects tend to be covert in their Aspect and, while they are the least powerful magics that can be used to directly influence a mage’s environment, they are still able to do just that. A clever willworker with only one dot in a given Arcanum can still use Compelling spells to great effect, especially if she has already learned the lay of the land, as it were, with Knowing and Unveiling magics.
Discerning teachers of the Arcana tend to spend a good deal of time educating their students about Compelling spells and their effects, since they are, more or less, the “baby steps” of magics intended to alter phenomena in the Fallen World. Without first learning how to properly make a candle flame burn a little brighter or a little hotter, for example, a willworker will never be able to exert the degree of control necessary to defy gravity or vanish from sight. Also, most mentors see such teaching as a good way to get a handle on a student’s proclivities as a mage, beyond just the magics favored by her Path. How an Apprentice uses Compelling magic says a great deal about how she intends to use mightier magics when they are at last within her grasp.