The idea of epilepsy as a disease per se.

In the 1850s Delasiauve and Russell Reynolds independently introduced the idea that the previously more inclusive concept of "epilepsy" should be restricted to that of an idiopathic disease manifesting epileptic seizures not caused by detectable brain pathology. This idea was rather widely accepted, though with some modification, over much of the next century. However there was increasing opposition to the idea from those, including John Hughlings Jackson, who perceived that all epileptic seizures must be symptoms of underlying brain disease. With increasing identification of structural brain pathology in what had been regarded as instances of idiopathic epilepsy, the latter view has increasingly prevailed.