This Master's thesis concerns the professional knowledge of the librarian. The image of this knowledge is regarded as constructed in a social context, which is why the discourse analytic approach is selected as method. The empirical material consists of two texts concerning the education of librarians. A theory of knowledge, emanating from Aristotle, is applied to the results to find examples of the forms of knowledge that are excluded from the discourse. A number of themes, or ways, in which it is possible to discuss the phenomenon of the librarian's knowledge, are identified in the texts. The results also show the consequences, for the discursive constitution of the librarian's knowledge, of an antagonistic relation between two discourses. The application of the theory of knowledge reveals that the discourses exclude the possibility of constituting the librarian's knowledge as phronesis, ethical knowledge.