This article begins by reviewing the history of etiologic thinking in the field of temporomandibular disorders (TMD). I conclude from this review that not only are the old mechanistic etiologic concepts incorrect, but also that 2 of the most popular current concepts (biopsychosocial and multifactorial) are seriously flawed. Therefore, what we really have at the individual TMD patient level is nearly always an idiopathic situation--we simply do not know enough, or cannot measure enough, or cannot precisely determine why each patient has a TMD. In addition, we do not understand the host resistance factors that ultimately determine why one person gets sick while another does not. The issue of "why" (etiology) must be differentiated from the issue of "how" (pathophysiology), both semantically and intellectually, to discuss all of this properly. However, our current inability to precisely identify etiologies in TMD patients does not prevent us from providing sensible (and often successful) treatment for most of these patients. Many health conditions currently are treated by physicians and dentists with either incomplete or flawed understanding of their etiology, but the availability of empirical data about treatment outcomes permits some level of appropriate care to be given. Fortunately, a large number of comparative studies have been done in the field of TMD therapy, providing us with a basis for selecting initial therapies as well as for dealing with treatment failures. Even in the absence of a perfect understanding of etiology, we still can provide good conservative care, and we should avoid aggressive and irreversible treatments, especially when they are based on flawed concepts of etiology. The article concludes by discussing current basic science research activities in the field of TMD and orofacial pain. I propose that these ongoing studies of the molecular and cellular mechanisms of joint disease, muscle pain, and chronic pain are the most likely avenues to future progress in this field, as specific countermeasures are developed to become the basis for more precisely targeted therapies.