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
I prepare tax returns for small businesses in Surrey, and 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…
Started by Harpreet Kaur Grewal3 replies126 views -
Why does the muddy children puzzle need the parent’s announcement if every child already knew?
I design puzzle games for a small studio in Tainan, and a colleague 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…
Started by Huang Wei-ting3 replies206 views -
What do Prior’s four tense operators actually say, in plain words?
I design puzzle games, and the one 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…
Started by Huang Wei-ting5 replies163 views -
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 Huang Wei-ting4 replies124 views -
My rice cooker says ‘fuzzy logic’. Is that just probability with a nicer name?
I run a kitchen in Dubai, twenty-two cooks from nine countries. We bought a Japanese rice cooker with "Fuzzy Logic" printed on the front, and it has become a running joke. The Filipino line cook says the rice is "fuzzy done". The…
Started by Joel D'Souza4 replies160 views -
“Not necessarily” versus “necessarily not”: can someone explain the difference with an everyday example?
I left accountancy to raise two children, and the older one (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…
Started by Thamarai Selvi Raman4 replies216 views -
Newton da Costa and why paraconsistency has a Brazilian accent
Newton da Costa died in 2024, and I've wanted to write something about him for the forum since. For anyone outside Brazil: he built the first systematic paraconsistent logics, logics in which a theory can contain a contradiction without every statement becoming…
Started by Ana Clara Ferreira5 replies246 views -
Syādvāda is not a seven-valued logic, and treating it as one loses the point
I grew up Jain and run a pharmacy in Ahmedabad, so I've been hearing about anekāntavāda since before I could read. Lately I keep seeing syādvāda described online as "the ancient Indian seven-valued logic", usually in the same breath as fuzzy logic.…
Started by Hetal Shah5 replies185 views -
Our safety manual tells us what to do after we’ve broken a safety rule. Is that a paradox?
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…
Started by Hugo Marchetti4 replies190 views -
What are the seven “in some respect” predications of syādvāda, and is it really a many-valued logic?
I work on many-valued and modal logics, and 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…
Started by Tomasz Wójcik4 replies198 views -
If you had to give up one classical principle, which would you choose?
Physics graduate here, now teaching. 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…
Started by Emeka Nwosu6 replies168 views -
Is Nyāya tarka a kind of counterfactual reasoning, and does it need possible worlds?
I teach mathematics, and when I read 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…
Started by Vikram Sethi5 replies228 views -
Can someone explain Ibn Sina’s propositions that are necessary ‘as long as’?
I model oil reservoirs, and 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…
Started by Abdulrahman Al-Qahtani5 replies175 views -
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 replies230 views -
Reading Nāgārjuna as a dialetheist imports a problem he did not have
I'm working on Madhyamaka and Nyāya debates for my MA, and I keep running into Graham Priest's reading of Nāgārjuna, partly in his own books and partly in the paper he wrote with Jay Garfield on Nāgārjuna and the limits of thought.…
Started by Meera Kulkarni5 replies162 views -
I use modal logic at work every day, and the engineers around me have no idea it was philosophy
I write formal-verification tools for chip designs in Austin. Every day my colleagues write properties like "on every path, whenever a request is issued, a grant eventually follows". In our notation that's something like AG(request → AF grant): A for "on all…
Started by Derek Hollis0 replies68 views -
The five rulings, from obligatory to forbidden: why the middle categories are not just extra boxes
Standard deontic logic has three basic statuses: obligatory, forbidden, and permitted. Anything neither obligatory nor forbidden is simply permitted, and that's the end of it. Islamic jurisprudence has five rulings (al-aḥkām al-khamsa). An act is obligatory (wājib), recommended (mandūb), permissible (mubāḥ), disliked…
Started by Khalid Mahmood Awan5 replies166 views -
Chisholm’s contrary-to-duty paradox: why exactly do four sensible sentences become inconsistent?
I litigate housing cases 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. Remedies, in…
Started by Thandeka Mokoena3 replies166 views -
Strong Kleene, weak Kleene, Łukasiewicz: what actually differs between the tables?
I build machine learning systems, and 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…
Started by Pieter de Jong4 replies218 views -
The sea battle argument is a scope mistake, and Aristotle half saw it
Every year I teach chapter 9 of De Interpretatione to seventeen-year-olds, and every year somebody leaves the room a fatalist. So here is the case I make to them, and I would like it attacked by people who know more logic than…
Started by Giulia Ferrante4 replies110 views -
Does the dialetheist really believe contradictions, or has she changed the meaning of ‘not’?
A question I keep returning to in my own work. 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…
Started by Tomasz Wójcik4 replies148 views -
Fuzzy logic is good engineering and a poor theory of vagueness
I've shipped fuzzy controllers. They work, they're cheap, and nobody who has used a decent one doubts that. My thesis is narrower: as an account of what vague words mean, fuzzy logic doesn't solve the problem it's usually advertised as solving. Two…
Started by Derek Hollis4 replies198 views -
How did Kripke’s possible worlds turn S4 and S5 from arbitrary axioms into something meaningful?
I'm a software engineer and 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…
Started by Pieter de Jong4 replies178 views