Many medieval authors are referred to by the name of Peter of Spain. One Peter of Spain is the author of a standard textbook on logic, Tractatus (Tracts), a work that became widely known as Summule logicales (Sum of logic) by magistri Petri Hispani and that would enjoy great renown in Europe for centuries to come. This work is typical of the manuals that gradually started to emerge within the context of twelfth- and thirteenth-century teaching practices.

With regard to the identity of this Peter of Spain, matters are rather complicated. Already in the Middle Ages there existed two traditions. One ascribed the Tractatus to a member of the Dominican Order (Black Friars), the other to the Portuguese secular priest who in 1276 became pope under the name of John XXI. The latter identification was favored until the latest research, done...