In order to determine who the wise man was and what the intelectual activity consisted in medieval times, we will suggest a semasiological, semantical and historical study of the adjectives 'sane' and 'expert' in four texts of the Castilian 13th century (Sendebar, Calila e Dimna, Barlaam y Josafat and the Libro de Apolonio). The objective is to determine the semantic area covered by both adjectives - etymological dictionaries do not always help us distinguish one notion from the other - and thus to find out to which extent the terminology present in these texts reflects the existence of various conceptions of knowledge, some of which therefore recently adopted.