A magical effect caused by "True Magick", the Enlightened effect of will on reality, that fits within the local Consensus and could be dismissed as coincidence. Coincidental magic does not incur paradox.
For Example: A ricochet off of a nearby pipe happens to hit the target, A jet of flame shooting out from a nearby pipe, an old man has a heart attack. Each of these effects could be coincidental, or could be the work of a will worker. By design and definition, coincidental magic can't be distinguished from coincidence.
Vulgar magic, by contrast, is obviously not coincidence. Stopping a bullet in mid air, hurling a fireball from an open palm, or draining the life from a healthy woman across the room are all vulgar effects.
Vulgar and coincidental are subjective, and often depend on the perspective of the consensus of the local area. a Verbena's health potion might be incredulous in a modern western city, but might go uncontested in a rural eastern European farming village, and could even be mundane in a Verbena shard realm.
There are multiple standards a Chronicle can use when determining if an effect is coincidental. M20 makes mention of two: Hypothetical Average Bystander and Hypothetica Omnicient Observer.
Hypothetical Average Bystander (HAB)Edit
Under this standard, an effect is considered coincidental if an average bystander for the area would not think something beyond possibility happened while observing the effect. Under this standard, using Matter and Prime to create a business card to hand to someone or teleporting it from elsewhere would be coincidental as it's reasonable that someone could do that. Circumstances could change this, as pulling a sniper rifle out of one's jorts would be vulgar (in multiple senses). HAB is the default assumption in the M20 rule set.
Hypothetical Omnicient Observer (HOO)Edit
Reality is everywhere and observing everything so all magic is noticed and considered vulgar. The exception to this would be cases where a reality zone were so thorough that the effect in question would be not only not impossible but expected as if it were a basic law of that reality zone.
A third standard is sometimes mentioned of Harrass Yonder Passerby and is often listed as a joke.
Notes on First EditionEdit
First edition Mage often had a much looser consideration of coincidental and was based on the results of the effect. If a mage used a matter effect to turn bullets into air, this effect could be considered coincidental by the gun having never been loaded. This standard is less common in contemporary play or at least not as flexible.