Prepositions are traditionally treated in dictionaries and grammars by giving a list of usages, often corresponding more or less to the way the preposition is translated in the language of the modern work. This paper suggests an alternative way of approaching prepositions, derived from cognitive linguistics where prepositions are regarded as categories centered on a salient prototype from which various peripheral members of the category are derived. This perspective has the advantage of presenting the meaning of each preposition as a unified category with a specific central meaning and various extensions, instead of merely listing a number of unrelated senses. It is argued that Middle Egyptian prepositions can fruitfully be studied in this framework, and the method is exemplified by examining the conceptual structure of the two frequent prepositions m and r.