This volume presents an English translation of Petrus Hispanus Portugalensis' (d. 1277) Tractatus - called afterwards Summulae Logicales - on the basis of the critical edition established by L. M. de Rijk (1972). The Summulae's first part (I-V) introduces Aristotelian ideas familiar enough at the time to be called Old Logic; the second (VI-XII) studies properties of terms, then considered novelties of Modern Logic. The two most important properties of terms were Supposition (meaning-as-reference) and Signification (meaning-as-sense). Among the questions raised were how senses and referents are related. Classifications recorded by Hispanus became part of Western traditional education. His Summulae was widely required as a text for generations, and later texts borrowed, amended, rejected or extended parts of it. The Summulae is also worth evaluating in the light of debate about the 'scientific' status of Linguistics. Hispanus claimed Dialectic was a study prerequisite to all others, because it shows how to test their fundamental assumptions. Norms he proposed for this rigorous interpretation of language are public, refutable, and countable, all characteristics claimed for 'science'.