Leading philosophical accounts presume that Thomas H. Morgan’s transmission theory can be understood independently of experimental practices. Experimentation is taken to be relevant to confirming, rather than interpreting, the transmission theory. But the construction of Morgan’s theory went hand in hand with the reconstruction of the chief experimental object, the model organism Drosophila melanogaster . This raises an important question: when a theory is constructed to account for phenomena in carefully controlled laboratory settings, what knowledge, if any, indicates the theory’s (...) relevance to phenomena outside highly controlled settings? The answer, I argue, is found within the procedural knowledge embedded within laboratory practice. †To contact the author, please write to: Minnesota Center for Philosophy of Science, University of Minnesota, Department of Philosophy, 831 Heller Hall, 271 19th Ave., University of Minnesota, Minneapolis, MN 55455‐0310; e‐mail: [email protected]. (shrink)

The concept of mechanism is analyzed in terms of entities and activities, organized such that they are productive of regular changes. Examples show how mechanisms work in neurobiology and molecular biology. Thinking in terms of mechanisms provides a new framework for addressing many traditional philosophical issues: causality, laws, explanation, reduction, and scientific change.