Professor de Rijk's interest here is in the views on reality put forward by the medieval thinkers from Boethius to William of Ockham, but especially in the 12th-14th centuries, the period from Abelard onwards.Theology was naturally a key influence, but sematic theories - the philosophical theories on how terms signify, or how a name has its meaning and how this is affected by its context - were fundamental as the starting point of ontological speculation. The categories formulated in order to differentiate various types of context and their impact on the semantics of the verb esse, 'to be', and its related forms. De Rijk's aim is to understand how these medieval thinkers interpreted reality according to their own semantic views, and to see how their own particular concerns - for instance William of Ockham's application of the 'principle of parsimony' to ontology - shaped the nature of their thought.