why did the bridge fall? it's a harder questions than it seems to be, and it already seems like a really hard question. let's say we put to one side the ponderous constraints on what even an engineer can know about the precise empirical facts of something even just as complicated as a bridge. say we know with perfect certainty the properties of all the materials the bridge is made of, and of all the pressures those materials will come under, and all of the effects that each part of the bridge will have on the other parts, and precisely what effects the environment will have on the whole structure. say we know the story of every raindrop that ever winds its way into any fissure in the concrete, or along any rivulet formed in the bend of the steel. say that there is no detail in the story of the epoxy and its corroding effects on the particular material of which the screws are made when the temperature falls below zero that escapes our notice. say the whole story of the bridge and the bridge's coming to fall is, in all of its immense complexity, fixed and knowable and known.
why did the bridge fall? you might think that under these conditions we have an answer to the question, but it turns out that we only have a story-- a long story of materials and dynamics in which each and every material and dynamic plays an ineliminable role. to pick out a part of the story, a particular material or dynamic, and say 'here is the cause' requires something else-- something more even than the most perfect knowledge. even more, that is, than what we can ever hope to have.
coming soon: proximate cause, making the difference, and everything that's left unclear, even then.