Category
Logic & argument
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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 -
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 -
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 -
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 -
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 -
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 -
Soundness and completeness of a logical system: what exactly is being proved?
I'm stuck on vocabulary, having no formal training in logic. I've read that a logical system can be sound and complete: everything provable is true, and everything true is provable. Fine. But then I read that Gödel proved a completeness theorem in…
Started by Pieter van Dijkhuizen4 replies -
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 -
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 -
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 -
Boole, not Frege, deserves to be called the father of modern logic
I'll declare my bias at the start: George Boole was professor of mathematics at Queen's College here in Cork from 1849 until his death in 1864. There's a plaque. I walk past it. Philosophers tend to say that modern logic begins with…
Started by Siobhán KeaneReply first (no replies yet) -
Logic for beginners: what makes an argument valid
A first introduction to the single most useful idea in logic, with the tests you can use on any argument and the mistakes almost everyone makes.
Started by The EditorsReply first (no replies yet)