There is a long-standing debate about the principles constraining the combinatorial properties of suffixes. Hay 2002 and Hay & Plag 2004 proposed a model in which suffixes can be ordered along a hierarchy of processing complexity. We show that this model generalizes to a larger set of suffixes, and we provide independent evidence supporting the claim that a higher rank in the ordering correlates with increased productivity. Behavioral data from lexical decision and word naming show, however, that this model has been one-sided in its exclusive focus on the importance of constituent-driven processing, and that it requires supplementation by a second and equally important focus on the role of memory. Finally, using concepts from graph theory, we show that the space of existing suffix combinations can be conceptualized as a directed graph, which, with surprisingly few exceptions, is acyclic. This acyclicity is hypothesized to be functional for lexical processing.
