When disorders fade into normality, how can the threshold between normality and disorder be determined? In considering mild intellectual disability, I argue that economic factors partly determine thresholds. We tend to assume that the relationship between disorder, need and services is such that: first, a cut-off point between the disordered and the normal is determined; second, a needy population is identified; and third, resources are found (or at least should be found) to meet this need. However, the changing definitions of intellectual
disability can best be understood if we think of this happening in reverse. That is, first, certain resources are thought obtainable, and then a cut-off point for disorder is selected which supplies an appropriately sized ‘needy population’.