In this article I discuss the nature and function of scientific concepts, what ittakes to possess them, how they can be represented, and how they can be studiedby examining the uses of the scientific terms associated with them. I then examinethe epistemological issues that arise when considering conceptual change.Furthermore, I draw a distinction between concepts referring to manifest entities(accessible to observation) and concepts referring to hidden entities (temporarilyor permanently unobservable). I argue that the function of scientific concepts isdifferent in the two cases. In the former case, their function is primarily classificatory;whereas in the latter case, their function is primarily explanatory. Finally,I suggest that the epistemological problems generated by the evolution of scientificconcepts are more severe in the latter case than in the former.

The author brings out the many faces of explanation in history of science by commenting on the contributions to a Focus section of Isis on historical explanation. The essay starts by indicating several ways in which the term “explanation” is used in historiographical discourse. It then distinguishes the object of explanation from the process of explanation and points out common themes and points of contention among the thirteen contributions. It also discusses two of those points in more detail: the problems of causal explanation in history of science and the imperative of avoiding anachronism in historical interpretation. The essay concludes by suggesting a pluralist take on explaining science historically.