Category
Logic & argument
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What’s the difference between a valid argument and a sound one?
In a debate thread here someone said an argument was "valid but not sound" and I realised, being completely new to logic, that I didn't understand the difference. To me both words just sounded like "good". Could someone explain simply, with examples…
Started by Kavya Menon3 replies -
Fes, al-Qarawiyyin, and how medieval students learned to argue
Al-Qarawiyyin is a short walk from my school. 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 Berrada2 replies -
How does one contradiction let you prove absolutely anything?
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 a king, anything. This sounds like a trick. Contradictions are bad, sure, but why…
Started by Fajar Nugroho3 replies -
What do the strange names Barbara, Celarent and Darii actually mean?
I'm 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 Baroco. The book just says…
Started by Fajar Nugroho4 replies -
Quine was right that even logic could be revised in the light of experience
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. The picture: our…
Started by Ethan Mercer6 replies -
Why does logic count ‘if the moon is cheese, then 2 + 2 = 5’ as true?
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 false only when P…
Started by Gemma Pritchard4 replies -
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 Szewczak4 replies -
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 replies -
What is “defeasible” reasoning, and why do people say most good arguments aren’t valid?
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 I reason all day. The…
Started by Joel D'Souza4 replies -
The Nyaya five-membered syllogism versus Aristotle’s three
I've recently started comparing two traditions of logic. 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 in a kitchen.…
Started by Vikram Sethi4 replies -
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 replies -
Every invoice needs some approver: why does the order of quantifiers change the meaning?
One of my clients, a small business, has an internal policy that 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…
Started by Harpreet Kaur Grewal4 replies -
My debaters say ‘if the moon is cheese, then 2 + 2 = 4’ is true. Are they right?
Two of my sharper debaters 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 is true. And "if…
Started by Sam Ellery4 replies -
Keep the losing opinion on the page: what the Talmud could teach an online forum
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 see here. Record the minority view. The Mishnah asks why it bothers…
Started by Eliana Halpern6 replies -
Logical pluralism is right, for the same reason statistical pluralism is
In data science 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 the same. Carnap said something like…
Started by Wanjiru Njenga5 replies -
What is pragma-dialectics, and what makes a “critical discussion” different from ordinary arguing?
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 comes from Frans van Eemeren and Rob…
Started by Deepa Kartha4 replies -
Reading group: Toulmin’s The Uses of Argument, starting from the middle
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 of Argument (1958; the Cambridge updated edition…
Started by Sam Ellery6 replies -
How can I tell an argument is valid when I don’t know what its words mean?
Forgive me if this is basic; I'm very new to formal philosophy. 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 blickets. All blickets are…
Started by Kavya Menon4 replies -
Charity is for evaluating arguments, not for reporting what people actually said
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 proves nothing about the strong one. I accept that.…
Started by Sana Rizvi6 replies -
Affirming the consequent on a hospital ward
My nephew is a medical student in Cairo, and listening to him describe his ward rounds I've realised that his teachers spend a lot of their time correcting a logical fallacy, and also committing it. A student says: if this patient had…
Started by Omar Ragab5 replies -
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 Kilbride5 replies -
Vitaṇḍā is not always illegitimate: a critic with no thesis can still be doing philosophy
There is one problem in Nāgārjuna I have been chewing on for a long time. The Nyāya tradition calls vitaṇḍā illegitimate: one party only attacks and never defends a position, so they risk nothing and cannot be wrong. That seems fair as…
Started by Nima Tsering Gurung7 replies -
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 replies -
Frege said logic is not psychology. A materialist would like a word
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. Husserl later made the anti-psychologism case at length in the Prolegomena…
Started by Priya Raghavan4 replies -
‘Killing robbers is not killing people’: the Later Mohists on inferences that fail
One passage in the Later Mohist texts 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 a kind of inference…
Started by Chen Yuting5 replies -
The Four-Seven Debate: what a sixteenth-century exchange of letters teaches about disagreeing well
My students know Toegye's face, not his argument. This year I tried teaching the Four-Seven Debate not as doctrine but as a model of how to disagree. The basics: from 1559 Yi Hwang (Toegye), already the most respected scholar in Korea, exchanged…
Started by Ji-woo Ryu4 replies -
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 replies -
Could a culture reason by different logical rules, or is that a colonial myth?
Every year a student in my lycée class asks me some version of this: "Is logic universal, or is it just how Europeans think?" The history makes the question sharp. In the early twentieth century, Lucien Lévy-Bruhl described so-called primitive peoples as…
Started by Khady Sène5 replies -
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 Theodoridis5 replies -
Nāgārjuna says he has no thesis. Is “I have no thesis” itself a thesis?
There is a question I keep returning to, the oldest one in the long argument between Advaitins and Mādhyamikas. In the Vigrahavyāvartanī, answering a critic who says his claim that all things are empty refutes itself, Nāgārjuna says (I paraphrase): if I…
Started by Arjun Iyer5 replies