In the paper we discuss the relation between fuzzy sets and thegraded membership and typicality effects found in the studyof concepts. After a short overview of the topic, we presentthree experiments, carried out using the same method but withdifferent situational contexts, which examine whether gradedmembership and typicality could be considered as independentfactors capable of influencing the performance of human par-ticipants involved in sentence verification tasks, or they aresomehow interrelated. The paper concludes with a generaldiscussion of the experimental findings and the problems theypose for models of concepts based on the theory fuzzy sets.