 In trying to establish what combination of premises form valid inferences he proceeds like Aristotle and develops lists or tables in which he can group the valid patterns. The basic sentences (2:1)–(2:4) combined with a simple categorical sentence as the second premise boil down to what we today know as modus ponens and modus tollens. This led some modern interpreters to think that Boethius was developing a sentential logic as the Stoics had done (Dürr 1951), but this idea has been rejected by more recent scholars (Obertello 1969, Martin 1991 and Speca 2001). Whatever Boethius thought he was doing, he was not trying to develop a sentential logic. This becomes obvious if one considers a more complex hypothetical syllogism, such as the following, which he accepts as valid: