Abstract

Abstract The Duhem?Quine thesis is generally presented as the radical underdetermi? nation of a theory by experimental evidence. But there is a much?neglected second aspect, i.e. the coherence or interrelatedness of the conceptual components of a theory. Although both Duhem and Quine recognised this aspect, they failed to see its consequences: it militates against the idea of radical underdetermination. Because scientific theories are coherent conceptual systems, empirical evidence penetrates, as it were, the periphery and allows the localisation of central, not just peripheral hypotheses. There is then no reason to deny the existence of crucial experiments. Both these ideas are denied in the Quine?Duhem thesis. A discussion of the famous Stem?Gerlach experiment and the role of fundamental physical constants shows, however, that localisation is not only possible but essential for the validity of scientific theories. Quine's famous ?latitude of choice? turns out to be severely restricted