  This Aristotelian model exercises enormous influence during the Middle Ages, and until at least the fourteenth century, medieval philosophers develop their own analysis of relational situations in terms of it. In this context, the most important medieval debates concern the precise nature of the properties or accidents that relate particular substances. Some philosophers, such as Peter Abelard and William Ockham, adopt a form of reductionism, according to which the properties in question are accidents falling under categories other than relation. Thus, according to Abelard and Ockham, when Socrates is similar to Theaetetus, this is to be explained in terms of particular qualities, say, their respective colors. Other philosophers, however, such as Albert the Great and John Duns Scotus, reject this form of reductionism, maintaining instead that relations are accidents of a sui generis type. Thus, according to Albert and Scotus, when Socrates is similar to Theaetetus, this is to be explained by a pair of accidents whose members are distinct from, and irreducible to, their respective colors.