The general chemistry of muscle contraction was elucidated early on from test-tube reconstitutions of function:1, 2 Myosin and actin form an ATP-dissociable complex; myosin is an actin-modifiable ATPase, and the free energy of ATP hydrolysis “pays for” any work performed in contraction. The central structural feature of contraction was discovered later:3, 4 In the vertebrate sarcomere, thick (myosin) and thin (actin + control proteins) filaments interdigitate to produce shortening without change in filament length. Finally came the macroscopic “law of force”:5, 6 The “tetanic” shortening force, and/or the rate of chemical energy dissipation, is proportional to the number of interactions between (myosin) cross-bridges and actin. Even together these great discoveries are not an explanation of how muscle works because it remains unknown how myosin, actin, and ATP, located as they are, produce a force at the microscopic level, or how this force is directed and timed to produce the behavior expressed by the macroscopic law. On the other hand, it is nowadays pointless to theorize about these unknown processes unless the theory springs clearly and naturally from these firmly-established central facts.