r/logic • u/bushcraftmanzynski • 16h ago
r/logic • u/gregbard • May 21 '24
Meta Please read if you are new, and before posting
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This group is about the scholarly and academic study of logic. That includes philosophical and mathematical logic. But it does not include many things that may popularly be believed to be "logic." In general, logic is about the relationship between two or more claims. Those claims could be propositions, sentences, or formulas in a formal language. If you only have one claim, then you need to approach the scholars and experts in whatever art or science is responsible for that subject matter, not logicians.
"Logic is about systems of inference; it aims to be as topic-neutral as possible in describing these systems" - totaledfreedom
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Recreational mathematics and puzzles may depend on the concepts of logic, but the prevailing view among the community here that they are not interested in recreational pursuits. That would include many popular memes. Try posting over at /r/mathpuzzles or /r/CasualMath .
Statistics may be a form of reasoning, but it is sufficiently separate from the purview of logic that you should make posts either to /r/askmath or /r/statistics
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r/logic • u/Big_Move6308 • Jul 06 '26
Meta Free Online Logic Resources
The r/logic wiki now includes free online resources to learn logic (courses, books, and proof tools).
If you know of any others, please provide links so they can be added in future.
r/logic • u/yosi_yosi • 12h ago
Propositional logic My first substack article
Hello, this is my first substack blog post. It is kind of short and weirdly written, but I still would appreciate any thoughts.
Edit: the article's title is: "If AND is like Multiplication and (X)OR is like Addition Then What is Division?" And it is basically about finding an operator or function that would be analogical to division but for propositional logic (supposing AND is multiplication)
r/logic • u/TrainerOk717 • 19h ago
Philosophical logic Program in Formal Philosophy
Hi. I'm 13 and I study analytic philosophy. I'm building a multiparameter method for evaluating philosophical schools: Φ⁺ for macro-philosophy (ontology, modality, fundamentality) and Φ⁻ for micro-philosophy (epistemology, ethics). A prototype of Φ⁺ already exists (LaTeX document, working formula, pilot on Platonism/nominalism/structuralism).
I'm looking for:
Logicians — to formalize consistency conditions for Φ⁺ and Φ⁻.
Philosophers — to independently score 3–5 schools (inter-rater reliability).
Programmers — to build a small calculator for weights and sensitivity analysis.
Critics — to stress-test the method with counterexamples.
Systematizers — to organize parameters, scales, and documentation.
This is not "philosophy is fully formalizable." It's "evaluation can be structured" if we separate levels, declare normative assumptions, and calibrate on classic schools.
If interested — DM me. Age 13–22, but what matters is willingness to argue and check.
r/logic • u/If_P_Then_Panic • 1d ago
Philosophy of logic The Illusion of Meaning: Is Math Just Playing with Dashes?
Episode 1
Let's start with three completely meaningless symbols: p, q, and - (a dash). In Chapter 2 of Gödel, Escher, Bach, Hofstadter introduces a formal system called the pq-system, which does nothing but blindly shuffle these characters based on a few basic typographical rules. Imagine a machine completely devoid of understanding, just churning out strings like --p---q-----.
This is exactly where the magic of human cognition—and the core concept of isomorphism—kicks in. Our brains detect a pattern. If we map p to "plus," q to "equals," and treat the dashes as numbers, that sterile string suddenly snaps into a universal truth: 2+3=5. We project form and meaning onto lifeless symbols.
Hofstadter uses this to demonstrate that meaning isn't an intrinsic property of symbols. It emerges from discovering the structural correspondence between formal systems and reality. Meanwhile, the system's rules couldn't care less about our interpretations; the mechanism grinds on exactly the same way whether we see it as profound mathematics or just a tally of apples and oranges.
What are your thoughts on this? Don't these striking isomorphisms suggest that math actually resides in its own independent, abstract realm, making our formal systems nothing more than the nets we weave to catch those pre-existing truths?
— If_P_Then_Panic
r/logic • u/Interesting_North293 • 2d ago
Philosophy of logic Frege, can we say A=A is mandatory a priori?
A=A or "Hesperus is Hesperus” simply mean the same thing; therefore, it is analytical and a priori.
But if we say,
"(This) Odyssey is (the) Odyssey."
Can we count that as a priori too? Or is it both analytical and synthetic?
r/logic • u/bill_vanyo • 2d ago
Paradoxes Special pleading is a fallacy except in the case of this sentence.
It was intended jokingly, but how would you analyze the sentence: "Special pleading is a fallacy except in the case of this sentence"?
r/logic • u/Savings_Astronaut630 • 2d ago
Propositional logic Need help understanding Polish Notation
Hello, I’ve recently started studying mathematical logic on my own and came across a problem I had with a textbook I was reading (introduction to mathematical logic Mendelson second edition) the excersize in question asked me to write (C v ((B ^ (~D)) ⊃ C )) in Polish notation. I came up with the answer vC ^ B ~D ⊃ C.
However according to the book the answer is v C ⊃ ^ B ~DC. I’m very confused how it could come to that answer and the book itself is pretty old so I haven’t been able to google a proper answer. Would someone be willing to explain to me both how I got it wrong and the steps that it takes to annotate the problem properly? Thank you in advance.
r/logic • u/mushiyoo • 2d ago
Philosophy of logic Theological question about limits of human use of logic
If we claim that logic has limits when speaking about God, what logical grounds justify that claim?
TLDR: On empirical grounds we can reasonably justify that human use of logic is restricted and has limits when talking about Allah, Blessed Be He and may He bless and greet His Final Messenger Muhammad ﷺ.
r/logic • u/SineCosine8 • 2d ago
Computability theory Questions on the asymptotic limits of an algorithmic state-space damping heuristic
I am analyzing a parameterized dynamic scaling function designed to model state-space transitions. The heuristic function is formulated as f(n) = 2^(n / ((p(n))^2 * (3n+1))), where p(n) is a strictly increasing prime-product (primorial n#) and (3n+1) is a linear dynamics operator. Asymptotically, as n approaches infinity, the exponent collapses to 0, forcing f(n) to achieve absolute convergence to 1.0 at a super-exponential decay rate of O(e^(-2n)). I am trying to formalize its implications on a Nondeterministic Turing Machine (NDTM) configuration tree under a proposed Dynamic Branching Law, B(n) = 2^(f(n) - 1), where the compression drives the effective branching factor to exactly 1.0 in the limit. I would highly appreciate structural feedback from the logic community on these points: 1. Is the first-order asymptotic decay bound of O(e^(-2n)) derived via Taylor expansion robust enough to mathematically bound non-deterministic expansion? 2. Does an asymptotic compression of a branching factor to 1.0 formally imply a structural reduction of the search space, or is it isolated as a non-constructive mathematical artifact? 3. Which intermediate automata-theoretic or resource-bounded information frameworks are best suited to formalize these structural bottlenecks? Thank you for your time and guidance!
r/logic • u/superamerr • 3d ago
Paradoxes Is there a hardest question?
Suppose a hardest logically solvable question H.
Asking if H is the hardest question could then become H
But then we can repeat the process again, since "Asking if H (original) is the hardest question" is now our new H we can just do the same to it, then the same to the new one and over and over again.
r/logic • u/thoughtframeorg • 2d ago
Philosophy of logic Math Has Limits We Can Never Cross: Some truths are real even if we can never prove them.
r/logic • u/logbybolb • 4d ago
Literature "On the Hierarchy of Natural Theories" by James Walsh. Excellent survey on some modern research in mathematical logic
cambridge.orgr/logic • u/Automatic_Good4382 • 3d ago
Academic Community ANU Logic Summer School 2026 – Looking for Male Roommates in Canberra
r/logic • u/TrainerOk717 • 3d ago
Philosophy of logic From Logical Positivism to Formal Heuristics: What did the death of verificationism teach us about mathematical ontology?
r/logic • u/Southern-Invite-3481 • 5d ago
Propositional logic How to prove one conditional from another?
I'm doing some practice exercises in natural deduction, but the exercises don't come with an answer key, so I really have no clue how to figure this out:
A → (B → C). Therefore (A ∧ B) → C
I get as far as assuming A in a subproof, assuming B in a further subproof, and connecting A and B via conjunction introduction, but then I have no clue how to get back to showing that (A ∧ B) → C. What am I missing here? My thinking is that I need to prove that A and prove that B, so that if I assume their conjunction I can show that their conjunction implies C. But I have no idea how to do this in a way that allows me to cite the subproofs.
Any help is appreciated!
r/logic • u/TrainerOk717 • 4d ago
Philosophy of logic Why do we still treat Mathematics as "Ultimate Truth"? A critique of mathematical platonism and axiological bias.
r/logic • u/thoughtframeorg • 5d ago
Paradoxes Why 'Heap' Is a Word That Breaks Logic: Remove one grain of sand from a heap. Is it still a heap? Keep going.
r/logic • u/Tall-Lettuce206 • 7d ago
Set theory I wanted to see how a fully formalized theorem looks like. And I need to clear my understanding of proof structure. I have attached ZFC axioms and First order logic gentzen sequent calculus. So is it such that the proof trees of theorems have ZFC axioms in Gamma here?
additionally most undergrad math theorems like lagrange's subgroup can be written in this form?
Could I find atleast one theorem presented in such format?
And where all could the group axioms go? gamma or leafs?
r/logic • u/thoughtframeorg • 7d ago
History of logic How War Changed the Way We Use Logic: A soldier wrote a masterpiece while facing death in the Great War.
Logical fallacies Is there a fallacy for this?
If somone said this "Cant believe you wrote a dissertation on my one paragraph", in order to undermine my point or get a laugh from thier audience or to not put in effort to combat my point.
'Dissertation' would be very much hyperbolic.
Would i be gish galloping? I believe my points were succint to the best of my ability.
Question Question from my law school admission exam in Romania. Do you know any similar exams in your country? Im looking for more practice tests to solve
r/logic • u/1ByteIs7Bits • 9d ago
Literature Relearning logic from scratch, so I made a free book for myself (AI-drafted, needs real eyes on it)
Hi everyone,
I have a B.S. in Computer Science and really enjoyed the discrete mathematics course in my first three semesters. But I started working as a software engineer early, my focus drifted to IT-specific topics, and I never made my logic knowledge solid. Now I want to relearn it properly from scratch.
So I put together a self-study book for myself, drafted with an AI assistant, and I’m sharing it in case it helps someone else:
https://swicherwich.github.io/cogito-ergo-sum/
What’s in it: a “from absolute zero” part (reasoning, math language, sets and functions, a symbol atlas), propositional logic and natural deduction, predicate logic with careful treatment of the ∀/∃ rules, proof technique and induction, an overview of soundness, completeness and Gödel’s theorems, and a small Python proof checker and resolution prover with tests. It’s free (CC BY-SA) and works on phones, with dark mode and a dyslexia-friendly font.
Honest caveats: it hasn’t been reviewed by a logician, so there are probably mistakes, and the metatheory chapters are condensed rather than fully rigorous. If you spot an error or an unclear explanation, please open an issue: https://github.com/swicherwich/cogito-ergo-sum/issues
Again, hope it help somebody, and thank you for the feedback!