Early decisions to make in creating a magic system include what types of magic we want to include in the setting, how prevalent each is, what the source is, and whether mortals need spells to do it. These choices will guide everything that follows. Then we can consider the cost of magic to a practitioner and other limits. We should also decide if we’re inventing more than one type of magic for the setting and the limits of each, adding a name. With this in mind, we can then decide on training. We can invent specific spells, being careful not to craft many, if any, that solve a plot problem in a story we’re planning. Finally, we can invent local laws.