User Natalie Clarius

53 votes

Why should we care about syntactic proofs if we can show semantically that statements are true?

answered Aug 9, 2019 at 18:24

23 votes

Accepted

What exactly is a contradiction and how does it differ from falsity?

answered Oct 6, 2020 at 18:12

16 votes

Accepted

Why is $\{\emptyset\} \not = \emptyset$?

answered Oct 3, 2016 at 0:12

11 votes

Curious tautological pattern on"p->p"

answered May 29, 2020 at 17:58

11 votes

"Modus moron" rule of inference?

answered Mar 8, 2017 at 0:29

10 votes

Accepted

What is true about a proof system that is complete but not sound?

answered Feb 6, 2020 at 15:49

9 votes

Accepted

What is meant by 'weak' logic?

answered Aug 18, 2020 at 9:46

9 votes

Accepted

Syntactic proof that Peirce's law doesn't hold in simply-typed lambda calculus

answered Mar 21, 2019 at 14:02

8 votes

Accepted

How to compute CNF from truth table

answered Feb 17, 2020 at 14:14

7 votes

Can a conditional be both vacuously true and false?

answered Sep 2 at 16:08

7 votes

Commutative quantifiers

answered Mar 12, 2019 at 21:04

6 votes

Difference between $\forall xp(x) \vee \forall xq(x)$ and $\forall x(p(x) \vee q(x))$ in english?

answered Mar 3, 2020 at 15:02

6 votes

$ \models A$ vs. $ A \models$

answered Apr 27, 2020 at 19:45

6 votes

Accepted

Contexts in Natural Deduction

answered Jul 7, 2020 at 15:29

6 votes

The interpretation of $\nvdash$

answered Aug 9, 2020 at 20:49

5 votes

What are these symbols in logic called?

answered Sep 7, 2020 at 1:25

5 votes

Accepted

Are $\forall x\forall y(p(x,y)\leftrightarrow p(y,x))$ and $\forall x\forall y p(x,y) \leftrightarrow \forall y\forall x p(x,y)$ tautologies?

answered Jul 26, 2020 at 15:54

5 votes

Accepted

Does the language of the propositional calculus belong to some type of languages in Chomsky hierarchy (regular, CFL, CSL, recursive, r.e.)?

answered Jun 21, 2020 at 20:06

5 votes

Accepted

Is a reasoning valid when no rows where all premises are true in a truth table?

answered Mar 2, 2020 at 14:41

5 votes

Accepted

Does vacuous truth mean non-bivalent truth?

answered Mar 3, 2020 at 0:46

5 votes

Accepted

Natural deduction vs Sequent calculus

answered Jan 12, 2020 at 21:51

5 votes

Accepted

In what sense is logical entailment a set-theoretic relation?

answered Dec 3, 2020 at 10:28

5 votes

Accepted

Are quantifiers a type of logical connective?

answered Aug 1, 2022 at 15:41

5 votes

Accepted

What's the difference between $\vdash$ and $\vDash$?

answered Aug 25, 2019 at 20:16

4 votes

First order logic issue with the truth and scope of quantifiers

answered Jun 18, 2020 at 12:37

4 votes

Does mathematical logic have concepts for "validity" and "soundness" of "arguments"?

answered Jul 30, 2020 at 12:56

4 votes

Accepted

Differences between negations of two similar statements?

answered Aug 14, 2020 at 13:17

4 votes

Ex falso quodlibet with non well-formed formula or false interpretation?

answered Aug 8, 2021 at 4:24

4 votes

“$B$ does not follow from $A$” seems different from $\lnot(A\to B)$

answered Dec 2, 2020 at 17:15

4 votes

Variables vs. Constants, how are they defined in ZFC, and how they differ?

answered Dec 16, 2020 at 3:09

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347 Answers

Why should we care about syntactic proofs if we can show semantically that statements are true?

What exactly is a contradiction and how does it differ from falsity?

Why is $\{\emptyset\} \not = \emptyset$?

Curious tautological pattern on"p->p"

"Modus moron" rule of inference?

What is true about a proof system that is complete but not sound?

What is meant by 'weak' logic?

Syntactic proof that Peirce's law doesn't hold in simply-typed lambda calculus

How to compute CNF from truth table

Can a conditional be both vacuously true and false?

Commutative quantifiers

Difference between $\forall xp(x) \vee \forall xq(x)$ and $\forall x(p(x) \vee q(x))$ in english?

$ \models A$ vs. $ A \models$

Contexts in Natural Deduction

The interpretation of $\nvdash$

What are these symbols in logic called?

Are $\forall x\forall y(p(x,y)\leftrightarrow p(y,x))$ and $\forall x\forall y p(x,y) \leftrightarrow \forall y\forall x p(x,y)$ tautologies?

Does the language of the propositional calculus belong to some type of languages in Chomsky hierarchy (regular, CFL, CSL, recursive, r.e.)?

Is a reasoning valid when no rows where all premises are true in a truth table?

Does vacuous truth mean non-bivalent truth?

Natural deduction vs Sequent calculus

In what sense is logical entailment a set-theoretic relation?

Are quantifiers a type of logical connective?

What's the difference between $\vdash$ and $\vDash$?

First order logic issue with the truth and scope of quantifiers

Does mathematical logic have concepts for "validity" and "soundness" of "arguments"?

Differences between negations of two similar statements?

Ex falso quodlibet with non well-formed formula or false interpretation?

“$B$ does not follow from $A$” seems different from $\lnot(A\to B)$

Variables vs. Constants, how are they defined in ZFC, and how they differ?