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Our safety manual tells us what to do after we’ve broken a safety rule. Is that a paradox?

Hugo Marchetti Contributor
· 4 replies · 191 views
Modal & non-classical logicAnalyticModern European#contrary-to-duty#deontic-logic#rules#workplace-safety
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I drive a gantry crane at the container port in Marseille and I'm a union delegate, so I read the safety manual more carefully than most.

Rule 1: never enter the exclusion zone under a suspended load. Rule 2: if you find yourself in the exclusion zone, do not move; radio the operator and wait for instruction.

A colleague who reads philosophy told me this is an example of a "contrary-to-duty" obligation and that logicians have argued for sixty years about whether such rules can even be written down consistently. That surprised me. To us it is common sense: rule 2 exists because rule 1 will sometimes be broken, through fatigue, a mistake, a gust of wind.

So, a working man's question: is there something genuinely paradoxical here, or have the logicians tied themselves in a knot that we untie every day without noticing? And if there is a real problem, what is it in plain words?

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4 answers

  1. Johanna Reinhardt

    Fellow

    Not a paradox in practice, a problem in representation. Your manual works because everyone understands that rule 2 applies only in the situation rule 1 was meant to prevent. The difficulty for the logician is to capture "only applies once the first rule is broken" in a formal system where all the rules are true at once. Simple systems end up concluding that you both should and shouldn't do something. You untie the knot with context and timing, which the simple systems don't have.

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  2. Gerrit Venter

    Contributor

    Sport is full of these. Rugby's law says don't come in from the side at a ruck. If you do, there's a penalty, and if the penalty is cynical enough there's a yellow card, and then the team must play a man short. A whole tier of rules exists only for when the first tier is broken. Thirty years of coaching under-16s taught me that boys understand that structure perfectly well. It's the rulebook writers who struggle to keep it consistent.

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  3. Pieter de Jong

    Fellow

    Software engineer's version: exception handlers. The "happy path" code says what should happen; the handlers say what to do when it didn't. We write them in a separate layer, triggered by the failure, and they don't conflict with the happy path because they only run once it has failed. The logicians' fix (conditional obligations, often with time built in) is basically the same idea: the secondary duty is indexed to the situation after the breach.

  4. Hugo Marchetti

    Contributor

    Thank you. So the knot is real, but it is in the writing, not in the rule. That matters to me as a delegate: when management says a secondary rule "contradicts" a primary one, I'll ask whether they mean the rules conflict or only that they're hard to write down together.

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