Petty magic is a mishmash of minor spells, none of them particularly powerful, though some are distinctly unpleasant. Many are derived from the hedge magics that were the basis of most of the Empire's sorcery in the days before the teachings of Teclis; others were devised more recently for specific purposes. While not powerful, they are simple to cast, easy to control, and ideal for students to practise their magical techniques. For this reason, petty magic spells are taught to wizards' apprentices so that they can begin to understand the principles of magic. However, only the most useful and least harmful spells are considered to be suitable subjects of study.
Not all petty magic spells are innocent parlour tricks: there are several that definitely draw on Dark magic for their effects. These spells are generally less well-known and are rarely given to students; any master worth their salt will stay well away from them. Any apprentices who find themselves being taught Curse at the beginning of their magical career should have reason to suspect that their instructor is someone of whom they should be wary.