Descriptions of inflection classes usually take the form of broad or fine-grained (Stump & Finkel 2013) partitions of the set of lexeme, or link both in a hierarchic system of classes (Corbett & Fraser 1993; Dressler & Thornton 1996). Recent efforts to infer those automatically (Brown & Hippisley 2012; Lee & Goldsmith 2013; Bonami 2014) all rely on the assumption that the hierarchy takes the shape of a tree. We argue instead that semi-lattices, in which multiple inheritance is possible, are more appropriate to the modelling of inflection class systems. They capture directly the phenomenon of heteroclisis (Stump 2006), where different aspects of a lexeme’s paradigm relate it to different classes. We infer the semi-lattice using Formal Concept Analysis (Wille 1984) and describe a few measures of the canonicity of inflectional systems.