Summary For Thomas Edison, experiencing a failure did not mean that he had failed. Through an examination of the process that led to his invention of the carbon microphone, I argue that his positive approach to failure contributed both to his success as an inventor and to the functional success of his inventions. Edison's laboratory notebooks and legal testimony reveal that his seemingly erratic approach and reliance on trial and error methods in fact had a consistent direction and a rational (...) basis, well suited to the under-determined problems he faced. The outcome of this process, the carbon microphone, contributed significantly to the commercial success of the telephone and remains in use today. Thomas Hughes has observed that nineteenth century inventors made use of the unexpected behaviour of their inventions as sources of novel phenomena to exploit in new inventions. This paper identifies other ways in which Edison made use of failure and proposes that, paradoxically, the success of technological artefacts can be determined by the thoroughness with which failure is pursued in their creation. It also notes a parallel between Edison's instrumentalizing of failure and the way in which recent philosophers of science have proposed that scientists should make use of error. (shrink)