A note on a precursor of behavioral momentum.

This is a historical note on a precursor of the concept of behavioral momentum in the late 1950s and early 1960s, in particular, Charles B. description of it in terms of behavioral durability. The note is based largely on two email exchanges we had with John A. (Tony) Nevin, who offered insights on behavioral momentum as a term and a concept that are fit to be public on the occasion of this issue of the Journal of the Experimental Analysis of Behavior in his honor. Nevin addressed graduate work at Columbia University, the Newtonian analogy, the term behavioral momentum, and precursors of his work that are now lost in history. Ferster's description, though, was more compellingly modern than the others and the one first based in research on human operant behavior.