How scientists explain disease

In spite of its beguiling title and glowing blurb on the dust jacket, medical historians are likely to find this work remorselessly presentist, historically inaccurate and very hard going. It is the sort of book that gives philosophy of science something worse than a bad name. Besides the roller-coaster ride between technical philosophy and banal simplifications there is an unreconstructed realism here that will not appeal to modern historical sensibilities. Although lots of examples of the search for the causes of disease are given, the focus of the book is a supposed switch from humoralism to germ theory in the nineteenth century and the eventual explanation of peptic ulcer as caused by Heliobacter pylori. Thagard's endeavour is to generate a new, fairly eclectic account of how etiological ideas are produced by welding together writings from authors in the philosophy and sociology of science who would not, intellectually speaking, be seen within a million miles of each other. Beneath the surface of the approach, however, are a number of familiar assumptions. There are, we are told, at least three possible reasons why it is difficult to identify the causes of disease. First "there can be too many possible causes to sort out", as the history of scurvy at sea illustrates. Second is "background causal beliefs". For example "the recognition that beriberi is a nutritional disease was impeded by attempts to find a microbial cause". The third difficulty in identifying the causes of disease "is that many are not directly observable". So bacteria "became observable with the invention of the optical microscope" (p. 130). Even those who wish to write their history on these premises will find this book hard going.