  In the later 4th to mid 3rd centuries BCE, contemporary with Theophrastus and Eudemus, a loosely connected group of philosophers, sometimes referred to as dialecticians (see entry ‘Dialectical School’) and possibly influenced by Eubulides, conceived of logic as a logic of propositions. Their best known exponents were Diodorus Cronus and his pupil Philo (sometimes called ‘Philo of Megara’). Although no writings of theirs are preserved, there are a number of later reports of their doctrines. They each made groundbreaking contributions to the development of propositional logic, in particular to the theories of conditionals and modalities.