The professor begins by postulating three sets of bridge failures, with 3 being a subset of 2, and 2 being a subset of 1:
- all bridge failures,
- all bridge failures for which we can figure out what happened after it fell, and
- all bridge failures for which we could have predicted the failure ahead of time.
Spotty, this guy sounds like Donald Rumsfeld: There are known knowns, known unknowns, and unknown unknowns. Do you suppose he's obfuscating like Rummy?
We'll get into that in a moment, grasshopper. Wait—you know, you're right grasshopper—both the professor and Rumsfeld have that same eerie pedantic quality, don't they?
Then the professor says we know that the late 35W bridge was in the first set, but we don't even know if it is in set 2 yet, so how could it be in set 3?
Yeah, Spotty, how could it be in set 3?
As Spot pointed out in his linked post, without proper maintenance, every bridge is in set 3. Every one, failed and unfailed alike. In fact, if you accept the existence of a set 1—or assume it as the social "scientists" are wont to do—you've already lost the game. Here's the real world way to look at it:
- all bridges will fail if not maintained,
- it is uncertain as to how each bridge will fail, but it will fail eventually,
- a "vanishingly small" (to use the professor's term) proportion will fail in an unexpected way,
- the more heavily-traveled a bridge is, the greater the chance of its failure and the greater the consequences of that failure, and the public expects that vigilance and prudence will increase with the importance of a bridge,
- the proper husbandry of bridges is assumed by the public, in part because members of the public can't do it on their own, and
- the public will have a "vanishingly small" tolerance for screw-ups in the maintenance of bridges.
Look, boys and girls, we might find some absolutely stunning, unexpected physical explanation for the bridge failure. We could also, Spot supposes, find that it was bombarded by gamma rays from a cloaked Klingon warbird. But Spot thinks—and the public will, too—that ordinary malfeasance was afoot. The public is going to apply Louis Nizer's "rule of probability" and conclude that's what happened. Res ipsa loquiter.
Of course, the professor wants to talk about sets and uncertainty and risk, and he hopes to hell you'll buy the Klingon warbird theory. But just listen to, or better watch, Governor Pepsodent and Michael Brodkorb; they already know you won't.