String musicians, know only this: everything is vibrating. The movement of the spheres? A guru's cryptic musing? Hypersensitivity to plate tectonics? Not quite. This is the briefest possible distillation of Trager's Principle, which states, "When a string instrument is being played, everything is vibrating, from the top of the scroll to the tip of the endpin." This simple formula, the purest distillation of master luthier Chuck Traeger's lifetime...