‘Logic’ explains that logic has a broad and a narrow sense in Stoic theory and deals with a subset of sayables and meanings. Their logic is close to what we would call propositional logic. Chrysippus was the pioneer and genius of Stoic logic. He seems to have held that in simple assertoric logic all valid inference forms could be reduced to combinations of five basic and indemonstrable argument forms, with the assistance of several other logical and metalogical principles. The Stoics also worked extensively on modal syllogistic and other areas of research in logic with a sophistication not paralleled in some cases until the 20th century.