Two experiments were performed to investigate how people combine the truthfulness of component statements to judge the truthfulness of their conjunctions. In Experiment 1, 29 subjects judged the truthfulness of component statements and their conjunctions concerning class membership relation and scene. In Experiment 2, 34 subjects judged the conjunctions of artificial statements about class membership relation and about part-whole relation. The three rules for subjective conjunction were compared in terms of the theory of fuzzy logic. The overall results show that the minimum rule for fuzzy logical conjunction best approximates human conjunctions despite the types of statements.