Category
Logic & argument
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What’s the difference between a valid argument and a sound one?
I'm a literature student, completely new to logic. In a debate thread here someone said an argument was "valid but not sound" and I realised I didn't understand the difference. To me both words just sounded like "good". Could someone explain simply,…
Started by Kavya Menon3 replies3 views -
Boole, not Frege, deserves to be called the father of modern logic
I'm an accountant in Cork, and I'll declare my bias at the start: George Boole was professor of mathematics at Queen's College here from 1849 until his death in 1864. There's a plaque. I walk past it. Philosophers tend to say that…
Started by Siobhán Keane0 replies63 views -
Fes, al-Qarawiyyin, and how medieval students learned to argue
I take my students past al-Qarawiyyin every year. Founded in 859 by Fatima al-Fihri, it's often described as one of the oldest continuously operating institutions of learning in the world. What interests me is how teaching worked. Students learned not only texts…
Started by Youssef Benali2 replies147 views -
How does one contradiction let you prove absolutely anything?
I'm on a gap year and reading a lot, mostly al-Ghazālī and some existentialists. A friend studying computer science told me that in logic "a contradiction implies everything". If you accept one contradiction, you can prove the moon is green, that I'm…
Started by Fajar Nugroho3 replies163 views -
What do the strange names Barbara, Celarent and Darii actually mean?
I'm on a gap year and working through an old logic textbook my uncle left at our house. There is a page with a Latin verse that starts "Barbara, Celarent, Darii, Ferioque..." and then a lot of other names like Cesare and…
Started by Fajar Nugroho4 replies138 views -
Quine was right that even logic could be revised in the light of experience
Second-year undergraduate, so be gentle but not too gentle. We read the end of Quine's "Two Dogmas of Empiricism" (1951) in a seminar last week, and I think its most radical claim is correct: no statement is immune to revision, logic included.…
Started by Ethan Mercer6 replies274 views -
Why does logic count ‘if the moon is cheese, then 2 + 2 = 5’ as true?
I do stand-up, and half my jokes are conditionals. So I was pleased to find a whole branch of logic about "if". Then I hit the truth table and it broke my brain. Apparently in propositional logic "if P then Q" is…
Started by Gemma Pritchard4 replies175 views -
Can someone explain what the Nyāya logicians meant by vyāpti (pervasion)?
My training is entirely in Western formal logic, and I've started reading Matilal's The Character of Logic in India. I understand the standard example: there is fire on the hill because there is smoke, and wherever there is smoke there is fire,…
Started by Tomasz Wójcik4 replies179 views -
Nagarjuna’s tetralemma is not a rejection of logic
The catuṣkoṭi, or tetralemma, considers four options for any proposition: it is, it is not, both, neither. In the Mūlamadhyamakakārikā, Nāgārjuna often rejects all four. For example, the Buddha after death neither exists, nor doesn't exist, nor both, nor neither. Some readers…
Started by Meera Kulkarni4 replies155 views -
What is “defeasible” reasoning, and why do people say most good arguments aren’t valid?
I run a kitchen, and I read philosophy on the bus home. Last week I read that "most good real-world reasoning is not valid at all", and the word that kept coming up was defeasible. Here is my problem. In the kitchen…
Started by Joel D'Souza4 replies202 views -
The Nyaya five-membered syllogism versus Aristotle’s three
I teach logic to sixteen-year-olds and recently started comparing two traditions. The Nyāya inference for others (parārthānumāna) has five members: Thesis (pratijñā): the hill has fire. Reason (hetu): because it has smoke. Example (udāharaṇa): wherever there is smoke, there is fire, as…
Started by Vikram Sethi4 replies249 views -
Reading group: the first book of the Nyāya Sūtra with Vātsyāyana’s commentary
The Nyāya Sūtra, traditionally attributed to Gautama Akṣapāda and dated around the second century CE in its current form, is the root text of the school that made Indian logic and debate into a system. About three centuries later Vātsyāyana wrote the…
Started by Vikram Sethi6 replies207 views -
Every invoice needs some approver: why does the order of quantifiers change the meaning?
I do tax returns for small businesses. One client's internal policy says: "Every invoice must be approved by some manager." Two of their managers have now spent a month arguing about it. One reads it as: each invoice needs a manager's approval,…
Started by Harpreet Kaur Grewal4 replies156 views -
My debaters say ‘if the moon is cheese, then 2 + 2 = 4’ is true. Are they right?
I coach high-school debate. Two of my sharper students have discovered truth tables and are now using them against judges. Their favourite move: "if the moon is made of cheese, then two plus two is four" is true, because the second part…
Started by Sam Ellery4 replies175 views -
Keep the losing opinion on the page: what the Talmud could teach an online forum
I serve a congregation in Pittsburgh and teach Talmud on Tuesday nights. The more time I spend in online philosophy forums, including this one, the more I think the rabbis solved some problems we keep failing at. Three practices I'd love to…
Started by Rabbi Eliana Gutman6 replies232 views -
Logical pluralism is right, for the same reason statistical pluralism is
I build credit-scoring models in Nairobi. In my field the old fight between frequentist and Bayesian statistics has mostly cooled into pluralism: each is legitimate, they answer different questions, and a good analyst knows which to use when. I think logic is…
Started by Wanjiru Kamau5 replies172 views -
What is pragma-dialectics, and what makes a “critical discussion” different from ordinary arguing?
I'm a final-year law student in Delhi. In a moot court workshop a visiting lecturer kept referring to "pragma-dialectics" and "the rules for a critical discussion", as though everyone knew what they were. I nodded and didn't. From what I've gathered, it…
Started by Deepa Nair4 replies177 views -
Reading group: Toulmin’s The Uses of Argument, starting from the middle
I coach high-school debate in Portland, and the Toulmin layout (claim, grounds, warrant, backing, qualifier, rebuttal) is on every debate camp handout in the country. Almost nobody has read the book it comes from. Let's fix that. Text. Stephen Toulmin, The Uses…
Started by Sam Ellery6 replies168 views -
How can I tell an argument is valid when I don’t know what its words mean?
I'm a poet and very new to formal philosophy, so forgive me if this is basic. I met this pair of arguments in a logic primer: All whales are mammals. All mammals are warm-blooded. So all whales are warm-blooded. All zorps are…
Started by Kavya Menon4 replies206 views -
Charity is for evaluating arguments, not for reporting what people actually said
I cover courts and human rights in Karachi, and I keep running into a problem with the principle of charity. In philosophy the rule is good: before you object, reconstruct the argument in its strongest form. An objection to a weak version…
Started by Sana Mir6 replies219 views -
Affirming the consequent on a hospital ward
I teach medical students on ward rounds in Cairo, and I've realised that I spend a lot of my time correcting a logical fallacy, and also committing it. A student says: if this patient had pneumonia, she would have fever, cough and…
Started by Omar Farouk5 replies244 views -
Objections first: what the scholastic quaestio could teach a modern seminar
This term I've been reading the Summa Theologiae properly for the first time, article by article, and what has struck me is not the conclusions but the shape. Every article begins with “It seems that…” followed by objections against the position Aquinas…
Started by Aoife Brennan5 replies212 views -
Vitaṇḍā is not always illegitimate: a critic with no thesis can still be doing philosophy
I guide trekkers on the Annapurna circuit and read in tea houses in the evenings. A monk in Manang gave me a commentary on Nāgārjuna, and I've been chewing on one problem since. The Nyāya tradition calls vitaṇḍā illegitimate: one party only…
Started by Nima Tsering Gurung7 replies205 views -
Reading group: the Nyāya-sūtra on debate, from the sixteen categories to the points of defeat
Several threads here have touched on the Nyāya distinction between vāda, jalpa and vitaṇḍā. I'd like to read the primary text together, since most of us (me included, honestly) know it through summaries. Text. The Nyāya-sūtra attributed to Gautama (Akṣapāda), with Vātsyāyana's…
Started by Meera Kulkarni6 replies215 views -
Frege said logic is not psychology. A cognitive scientist would like a word
I work on perception in a cognitive science lab in Bengaluru. In the introduction to The Foundations of Arithmetic (1884), Frege lays down as his first principle that the psychological must be sharply separated from the logical, the subjective from the objective.…
Started by Priya Raghavan4 replies194 views -
‘Killing robbers is not killing people’: the Later Mohists on inferences that fail
My dissertation is on the Later Mohist texts, and one passage seems to me to belong in any discussion of what predicate logic was invented to handle. In the chapter of the Mozi usually called the "Lesser Selection" (Xiaoqu), the Mohists discuss…
Started by Chen Yuting5 replies267 views -
The Four-Seven Debate: what a sixteenth-century exchange of letters teaches about disagreeing well
I teach ethics at a secondary school in Seoul, where Toegye's face is on the 1,000-won note. My students know the face, not the argument. This year I tried teaching the Four-Seven Debate not as doctrine but as a model of how…
Started by Ji-woo Park4 replies258 views -
Dignāga cut the Nyāya inference from five members to three. What did the example member become?
I have been translating some passages on Buddhist logic for a seminar in Pune and keep getting stuck on one question. The Nyāya inference for others has five members: thesis, reason, example, application, conclusion ("this hill has fire, because it has smoke,…
Started by Meera Kulkarni5 replies206 views -
Could a culture reason by different logical rules, or is that a colonial myth?
I teach the final-year philosophy class in a lycée in Dakar, where Descartes and Senghor sit on the same exam paper. Every year a student asks me some version of this: "Is logic universal, or is it just how Europeans think?" The…
Started by Khady Faye5 replies161 views -
Reading group: Aristotle’s Metaphysics Gamma on the firmest principle
Several recent threads keep coming back to Aristotle's defence of the principle of non-contradiction, usually second-hand. Let's read it. It's short and much stranger than its reputation. Text: Metaphysics Book Gamma (IV), chapters 3 to 7. Ross's translation is freely available; Christopher…
Started by Nikos Stavridis5 replies209 views