Scientists typically do something other than accept or reject their theories, they pursue them. Throughout the greater part of the nineteenth century numerous chemists devoted their research energy and resources to the development of Daltonian theory, declaring themselves willing to make use of the atomic theory in their research but reluctant or unwilling to accept it. When Frankland, for example, declared that he did not want to be considered a “blind believer” in the atomic theory and could not “accept it (...) as true”, but that he had been—and planned to continue—using it “as a useful ladder”, he had arrived at a decision shared by many of his colleagues that while the theory was not acceptable, it was promising and worthy of pursuit.1 And when Van’t Hoff measured the kinetic-molecular theory by its fruits in the 1880’s, he judged that it barely gave the then-current 4% interest rate, and so was an unpromising theory, unworthy of pursuit (van Nelsen 1960. p. 151). (shrink)

Figuring prominently in their decisions regarding which theories to pursue are scientists' appeals to the promise or lack of promise of those theories. Yet philosophy of science has had little to say about how one is to assess theory promise. This essay identifies several indices that might be consulted to determine whether or not a theory is promising and worthy of pursuit. Various historical examples of appeals to such indices are introduced.

The foundations of modern organic chemistry were laid by the seminal work of Hughes and Ingold. The rise from being an interesting alternative hypothesis in 1933 to being the leading theory (outside the USA) in 1942 was achieved by a multiplicity of methods. This include:the construction of a new scientific notation, the rationalisation of some seemingly contradictory reported data, the refutation of the experimental work of one of their persistent critics, the use of conceptual arguments and also the achievement of (...) a score of successful predictions which exceeded the score of unsuccessful predictions. Within the USA it was felt that the Hughes/Ingold system, whilst representing a considerable advance, had achieved spectacular success in spite ofits attractively simple basic assumptions, and represented merely an interim stage on the way towards a more comprehensive theory. However,the flexible, simple notation was adopted without modification, leading to a change in the way practitioners of synthetic organic chemistry were, and still are, trained to think. In a conclusion the author claims that this historical episode does not lend any support to the philosophical position of Thomas Kuhn. (shrink)