1205 – 1277
Peter of Spain (Petrus Hispanus, c. 1205–1277) was a Portuguese scholastic philosopher, logician, and physician who later became Pope John XXI. He is best known for his Summulae Logicales, one of the most widely used logic textbooks in medieval European universities, which systematized Aristotelian logic and introduced influential terminology in the study of supposition theory and the properties of terms.
Authored the Summulae Logicales, the dominant logic textbook in medieval universities for over two centuries
Developed and systematized supposition theory, a key tool in medieval semantic analysis
Advanced the study of the properties of terms (proprietates terminorum) within Aristotelian logic
Served as Pope John XXI (1276–1277), the only Portuguese pope in history
Wrote medical treatises, including the Thesaurus Pauperum, reflecting his dual career in philosophy and medicine