When asked to indicate which items from a set of candidates belong to a particular category, inter-individual differences appear: Individuals disagree on the items that should be considered category members (e.g., Black, 1937; Hampton, Dubois, & Yeh, 2006; McCloskey & Glucksberg, 1978). Individuals might disagree about whether hiking and/or darts are sports, for instance. We will argue that inter-individual differences in semantic categorization come in two kinds. (i) Qualitative differences reflect a different organization of the candidate items with respect to the target category. (ii) Quantitative differences reflect a different propensity to endorse items as category members.