This paper deals with how the validity of a category describing a person's conception of a phenomenon is established. The presentation is confined to the relation between some categories of description and one interview protocol. The case described here is taken from an investigation into conceptions of political power. The description concerns how the thinking expressed in one interview may be found to represent several conceptions of political power described in the form of categories. The description of the analysis of the interview protocol concerns: selection of significant statements, delimitation of parts of the interview representing conceptions of power, the relation of the significant parts to the whole interview, the difference between the oral and the written version of the interview, and finally what is general to the approach of contextual analysis and what is specific to the present case. (Author/PN)