The physician Herophilus of Chalcedon, who lived and worked in Alexandria in the early third centuryb.c., is best known and justly celebrated for his numerous and ground-breaking anatomical discoveries and advances in such areas as pulse theory. His systematic investigations into the human body led to some of the highest achievements of Hellenistic science, among which the best known is probably his discovery and detailed description of the nervous system and its functions. Yet certain aspects of his thought have seemed (...) difficult to harmonize with the aims and methods of his medical research. One such is his attitude to causality. According to Galen, Herophilus had accepted the existence of causes merely on a hypothetical basis, and indeed had made the striking claim that ‘by nature it is not discoverable whether causes do or do not exist’. Galen associates these views directly with a number of arguments designed to prove that there are no such things as causes, but we are otherwise left with little in the way of context, and different interpretations have unsurprisingly suggested themselves. (shrink)