There are certain thought barriers involved in making diagnostic-classification criteria in diseases of unknown origin. Among these are a lack of appreciation of the issue of circular logic, the basic oneness of diagnostic and classification criteria, the lack of appreciation as to why we make such criteria in the first place, and the lack of importance informing our patients that we do as well as should treat them without a frm diagnosis in many instances. The relevance of these thought barriers to the new American College of Rheumatology/European Union League Against Rheumatism (ACR/EULAR) Rheumatoid Arthritis (RA) classification criteria are also discussed.