He divides them into three basic types, based on the motivation and ability level of the user: a facilitator trigger, which helps those with high motivation but low ability take action; a signal trigger, which helps keep people with high motivation and high ability headed in the right direction and encourages repeat action; and a spark, which spurs people with high ability yet low motivation to take action. Many email and mobile notifications fall into the “spark” category, but they shouldn’t be the only ones considered.
