By 1870, and within 5 or 6 years of his beginning to analyse the clinical phenomena of epilepsy and to correlate them with autopsy data, the 35-year-old John Hughlings Jackson had come to a view of the nature of epilepsy that was radically different from that of his contemporaries. He recognized that epileptic seizures arose in the cerebral cortex, and not in the medulla oblongata, as was then thought, and he saw that there was no fundamental difference between so-called 'genuine' epilepsy and epileptiform seizures. His great lecture, 'A study of convulsions', published in 1870, contains the essence of nearly all our modern ideas concerning the nature of epilepsy. While Jackson spent the next 30 years of his life in further interpretation of the phenomena of epilepsy, as he did this he began to back away from many of the more radical implications of his earlier brilliant insights. He seems to have done this to make his views more palatable to his contemporaries, but this also encouraged him to interpret varieties of epilepsy in relation to a conceptual scheme of 2, and later 3, hierarchal levels of nervous system functioning. The result is that today's reader of Jackson's later papers can be left rather bewildered and it is only by reading the whole corpus of his work that his enormous conceptual contribution to present-day epileptology can be appreciated.