  Logic is the art of discerning truth from falsehood and of making and judging arguments (ISW I 1.1; IGP I 1.1). The study of logic must therefore begin with the study of words. The Introductions, ISW and IGP, first define sounds, significant sounds, words, phrases (orationes), and sentences, then proceed to detailed discussion of complex hypothetical and categorical sentences and syllogisms. William's approach here became a model for twelfth-century logic textbooks.