Vulgar magic is an obviously magical effect caused by "True Magick", the Enlightened effect of will on reality. Vulgar magic incurs paradox. For example, hurling a fireball from an open palm is vulgar magic. Tossing a ball of pure flame, would be something pretty unbelievable to the Consensus. Even if no one was around to actively disbelieve, consensual reality would fight such an obviously intrusive event.