As a new discipline within the growing field of disciplines that deals with the design of information systems, information architecture (IA) is still struggling to define what this multi-disciplinary science or art is all about. The purpose of this thesis is to show that behind this discipline lies a rationality that makes IA one of the most important disciplines when it comes to designing information systems - a rationality that has its roots in the Roman rhetorical tradition and the way of thinking that this tradition represents. Starting with the ”user-experience”-model of Jesse James Garrett and a comparison of this model with other major contributors to the field, it is argued that IA on the one hand involves a narrow understanding of the design of information systems, perceiving the core of IA as a logical process of categorization and the goal of IA as that of supporting information retrieval. On the other hand, IA, it is argued, involves a broader perspective, perceiving IA as a discipline which basically is concerned with effective communication and therefore perceives the goal of information architecture as that of adapting the design to the context or ”information ecology”. Where the former seems to be based on a logical rationality it is argued that the latter is more ”ambiguous” and seemingly based on a rationality that involves intuition, creativity and common sense. Through a comparative analysis of information architecture and rhetoric I argue that information architecture at its core is best viewed as a rhetorical - not a logical, rationalistic - discipline and therefore should be rooted in the rhetorical way of thinking. This rationality and its relation to IA are further explored through the Roman rhetoric of rhetoricians like Cicero and Quintilian and the ”Latin humanist tradition” which, according to Ernesto Grassi, lies behind this rhetorical perspective. It is argued that this perspective, which does not separate form and content as opposed to the rhetoric of Plato and Aristotle, seems to ”fit” the reality that the information architect experiences - a reality where formalized and systematized methods cannot guarantee the successful design of an information architecture and where user tests and user evaluations - and thereby ”performance” - seems to be the only way to validate a design. Viewed from this rhetorical perspective, it is concluded that IA is a discipline requiring ”witcraft” - the ability to use common sense in a witty and creative manner - and this ability is rooted in ”ingenium” - the rationality that lies behind every ”original insight” into the relationship of things that is relevant to human beings.