The general aim of this study was to examine the relations among epistemological, reading and writing beliefs held by psychology undergraduates and the role played by these three types of belief in influencing the degree of perspectivism manifested in a written argumentation task based on reading two texts presenting conflicting perspectives on the same topic. A total of 118 fourth-year psychology students took part. Only 76 students performed the written argumentation task. The three types of belief were assessed using different questionnaires. The results show that the different types of belief do not occur in isolation, but have an internal coherence. They also indicate that only reading beliefs, together with the degree of perspectivism shown in a prior argumentation task, help to predict the degree of perspectivism in the written task following the reading of the texts.