Introductory essay / by Ian Hacking -- Preface -- Introduction: a role for history -- The route to normal science -- The nature of normal science -- Normal science as puzzle-solving -- The priority of paradigms -- Anomaly and the emergence of scientific discoveries -- Crisis and the emergence of scientific theories -- The response to crisis -- The nature and necessity of scientific revolutions -- Revolutions as changes of world view -- The invisibility of revolutions -- The resolution of revolutions -- Progress through revolutions -- Postscript-1969