Peter of Spain It is now thought that there were two Peters of Spain. The Spanish prelate and philosopher (c.1205–77) was born in Lisbon, studied at Paris, and taught medicine at Siena (1248–50). He served in various ecclesiastical posts in Portugal and Italy (1250–73) before being elected pope as John XXI in 1276. He wrote several books on philosophical psychology and compiled the famous medical work Thesaurus pauperum. The second Peter of Spain was a Spanish Dominican who lived during the first half of the thirteenth century. His Tractatus, later called Summulae logicales, received over 166 printings during subsequent centuries. The Tractatus presents the essentials of Aristotelian logic (propositions, universals, categories, syllogism, dialectical topics, and the sophistical fallacies) and improves on the mnemonic verses of William Sherwood; he then introduces the subjects of the so-called parva logicalia (supposition, relatives, ampliation, appellation, restriction, distribution), all of which were extensively developed in the later Middle Ages. There is not sufficient evidence to claim that Peter wrote a special treatise on consequences, but his understanding of conditionals as assertions of necessary connection undoubtedly played an important role in the rules of simple, as opposed to as-of-now, consequences.
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