 Collaborative work and discussion with Clinton Tolley, Scott Edgar, Gary Hatfield, Martin Kusch, Michael Heidelberger, Liesbet de Kock, and Francesca Biagioli, among many others, has made my grasp of Helmholtz’s views more precise. Discussions with Michael Forster on the methods of the natural and the human sciences provided valuable leads for that section. Thanks are due to Emily Carson, Michael Hallett, and Alison Laywine for their aid with my very early work on Helmholtz, and to Stephen Menn for suggestions for revisions. Link Swanson, M. Steinfels, Eric Schliesser, and David Hyder have recommended work and suggested corrections. Especial thanks are due to Clark Glymour for detailed and very helpful comments on the first draft of this entry. 