H. P. Grice explains the 'pons asinorum' to P. F. Strawson

pons asinorum is a bridgelike diagram proposed by Alexander of Aphrodisias in his commentary on Aristotle’s Prior Analytics. It was used as a study aid to show how to proceed from premises to a given conclusion. “In the later Middle Ages this diagram (with accompanying mnemonic verses to distinguish good connexions from bad) was used extensively for the teaching of syllogistim and came to be known as the pons asinorum.” Kneale and Kneale, The Development of Logic.