The current periodontitis paradigm embraces the idea of the existence of several particular disease entities. Among them, aggressive periodontitis has been defined as a particular form of periodontitis characterized by severe periodontal destruction usually affecting persons under 30 years of age and presenting with clearly identifiable clinical and laboratory features. Nonetheless, considerable het-erogeneity exists in the criteria used to identify the disease; only scant evidence exists substantiating the suggested distinct features; and several voices have expressed concerns on the suggested ad-vantages of considering aggressive periodontitis as a particular disease entity. The main explanation for this impasse can be found in the deep rooted belief that periodontitis is a group of particular clinical entities. This approach to periodontal disease is based on an es-sentialistic understanding of illness that obstructs advance in periodontal research. The use of a pragmatic nominalistic approach to periodontal dis-eases would provide a more rational framework for understanding periodontal health and disease and would easy the conduct of periodontal research. The implications of using a pragmatic definition of periodontitis are discussed.