Every instrument is a compromise between strength (strings are always trying to pull their instrument to pieces) and resonance: too strong a build and the sound is killed; then it might as well be an electric guitar, he says, looking at me over the top of his glasses. Too weak and it will fly apart. We wonder if there is an analogy with the great cathedral builders, who could not calculate the forces needed to keep up their spires, vaults and columns but with each great monument tested the limits of materials and design in the name of faith (and the sponsor).