An orthodox assumption in logic is that (declarative) sentences have exactly one of two values, true (1) and false (0). Many-valued logics are logics where sentences may have more than two values. Aristotle (De Interpretatione, chapter 9) was perhaps the first logician to countenance the thought that some sentences (future contingents) may be neither true nor false; Aristotle's ideas were discussed by many logicians in the Middle Ages. However, contemporary work on many-valued logics commenced with the work of the Polish logician Jan Łukasiewicz early in the twentieth century. One hundred years later there are many well-known many-valued logics, and the properties of such logics are well established. The logics have important philosophical applications (e.g., in articulating the views that some sentences are neither true nor false, or both true and false, or that truth comes by degrees). They also have important technical applications (e.g., in establishing...