Category
Modal & non-classical logic
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If I must file the return, must I file it or shred it? Ross’s paradox for a tax preparer
A client's son, who is studying philosophy, told me about something called Ross's paradox. As he explained it: in the standard logic of obligation, if you ought to do A, then it follows that you ought to do "A or B", for…
Started by Harpreet Kaur Grewal3 replies -
Why does the muddy children puzzle need the parent’s announcement if every child already knew?
A colleague at the studio showed me the "muddy children" puzzle. I love it and I don't understand it. Three children, each with mud on their forehead. Each can see the others but not themselves. A parent says: "At least one of…
Started by Hsieh Wei-ting3 replies -
What do Prior’s four tense operators actually say, in plain words?
The game I'm building now has a time loop: the player relives the same afternoon and has to work out what will happen, what already happened, and what has always been true in the loop. A friend who did a logic minor…
Started by Hsieh Wei-ting5 replies -
Why do philosophers say “in some possible world” instead of just “possibly”?
I design puzzle games, so I spend my days building small worlds with rules. When I started reading about modality I kept seeing sentences like "there is a possible world in which you became a dentist." Why not just say "you could…
Started by Hsieh Wei-ting4 replies -
My rice cooker says ‘fuzzy logic’. Is that just probability with a nicer name?
We bought a Japanese rice cooker with "Fuzzy Logic" printed on the front, and it has become a running joke in the kitchen. The Filipino line cook says the rice is "fuzzy done". The pastry chef says everything in the kitchen is…
Started by Joel D'Souza4 replies -
“Not necessarily” versus “necessarily not”: can someone explain the difference with an everyday example?
My older child, who is nine, has started catching me out on words. Yesterday I said "it won't necessarily rain at the picnic". She said, "So it necessarily won't rain?" I said no, that's different. She said, "How?" and I realised I…
Started by Thamarai Raman4 replies -
Our safety manual tells us what to do after we’ve broken a safety rule. Is that a paradox?
Working the cranes, I read our 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…
Started by Hugo Marchetti4 replies -
What are the seven “in some respect” predications of syādvāda, and is it really a many-valued logic?
Reading about many-valued and modal logics, I keep meeting the Jain doctrine of syādvāda in footnotes that call it "an ancient three-valued logic" or "a seven-valued logic". I am suspicious of both descriptions, but I don't know enough to say why. From…
Started by Tomasz Szewczak4 replies -
If you had to give up one classical principle, which would you choose?
I've been working through a list of non-classical logics, and each one gives up something different: bivalence (every statement true or false), excluded middle (P or not-P), explosion (from a contradiction, anything), or the assumption that every name refers to something. Thought…
Started by Emeka Anyaoha6 replies -
Is Nyāya tarka a kind of counterfactual reasoning, and does it need possible worlds?
Reading Nyāya, I am always delighted by how close their techniques are to the proofs I teach. One that puzzles me is tarka, which I have seen translated as "hypothetical reasoning", "suppositional reasoning" or "reductio". The classic example seems to go like…
Started by Vikram Sethi5 replies -
Can someone explain Ibn Sina’s propositions that are necessary ‘as long as’?
I started reading the history of logic because the Ash'ari material I love keeps assuming you know Ibn Sina. A survey chapter on Arabic logic lost me at one point, and I'd like a patient explanation. It says Ibn Sina split a…
Started by Abdulrahman Al-Bassam5 replies -
Why does my SQL query treat NULL = NULL as neither true nor false?
Beginner question from a data analyst. Last week a report of mine undercounted customers by about four per cent. The bug was a filter like WHERE region 'KL', which I assumed would return everyone outside Kuala Lumpur. It also silently dropped every…
Started by Nur Aisyah Rahman4 replies -
Chisholm’s contrary-to-duty paradox: why exactly do four sensible sentences become inconsistent?
I work for a tenants' organisation in Johannesburg, so most of my working life is spent on what is owed when someone has already failed to do what they should: the landlord who evicted unlawfully, the municipality that didn't provide alternative accommodation.…
Started by Thandeka Mokoena3 replies -
Strong Kleene, weak Kleene, Łukasiewicz: what actually differs between the tables?
I've been reading about how to reason with partially evaluated expressions, where some sub-expressions haven't been computed yet or failed. That led me to three-valued logics, and now I have three sets of truth tables on my desk that look almost identical.…
Started by Pieter van Dijkhuizen4 replies -
Does the dialetheist really believe contradictions, or has she changed the meaning of ‘not’?
A question I keep returning to. Quine, in Philosophy of Logic (1970), has a famous argument against "deviant" logicians. Suppose someone claims to accept a sentence of the form "P and not-P". Quine says: then whatever they mean by "not", it isn't…
Started by Tomasz Szewczak4 replies -
How did Kripke’s possible worlds turn S4 and S5 from arbitrary axioms into something meaningful?
I've been reading about modal logic for fun. I understand the operators. What I don't understand is the history I keep seeing summarised: C. I. Lewis invented several systems, S1 to S5, with different axioms; nobody could say which was "correct" or…
Started by Pieter van Dijkhuizen4 replies