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Questions tagged [symbolic-logic]

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proof for relational predicate logic

I have been working on this problem for over an hour and I think I have simply missed something. I need some help. The rules I am allowed to use are the Basic Inference rules (MP, MT, HS, Simp, Conj, ...
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5answers
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What would be an intuitive understanding of Peirce's law?

Wikipedia describes Peirce's law as In propositional calculus, Peirce's law says that ((P→Q)→P)→P. Written out, this means that P must be true if there is a proposition Q such that the truth of P ...
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language proof and logic chapter 13 question 49 Help

Premises: ∃xP(x) ∀x∀y((P(x)∧P(y)) → x = y) Prove: ∃x(P(x)∧∀y(P(y) → y = x)) I've started it but the end is starting to get super muddy and not work out and I don't know where I went wrong.
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4answers
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Symbolic Logic - Quantifier Proof (w/ Conditionals)

I'm not sure if lines 6 - 7 & 8 - 11 are being done correctly. I feel like it's necessary to prove 12 which proves the rest of the problem. I'm a bit stuck on lines 8 - 11. I initially tried to ...
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1answer
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Seeking clarification of how an argument from Aristotle is found fallacious using Frege's quantification tools

G. E. M. Anscombe writes in An Introduction to Wittgenstein's Tractatus (page 15-16): Again, the following fallacious piece of reasoning is found in Aristotle: 'All chains of means to ends must ...
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Fitch Biconditional Proof Help?

Hi, I'm starting to learn formal proofs using Fitch, but I'm having a bit of trouble figuring out my arguments. I've generally mapped out the subproofs I was considering to use, but I'm unsure how to ...
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2answers
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Can something proved by contradiction always be proved without a proof by contradiction?

Proof by contradictions work by assuming that something is true, and then using logic (along with other assumptions which you know are true) to show that that leads to a contradiction, thus proving ...
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3answers
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How to prove : (( P → Q ) ∨ ( Q → R )) by natural deduction

Here's another of Tomassi's exercises I can't solve (Logic, page 106): : (( P → Q ) ∨ ( Q → R )) I have to use natural deduction and the only rules I know are: • assumptions, • modus ponendo ...
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1answer
24 views

Conditional IFF - Not sure what's wrong

"Not a valid application of the rule" I don't think 7 - 8 is something that really needs to be proven beyond a reit but I feel like you should be able to... I'm quite confused on proving Cube(a) ...
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2answers
100 views

Symbolic Conditional Help

Premise: (Tet(a) ^ Tet(b)) v (Cube(c) ^ Cube(d)) Cube(c) -> Dodec(e) Goal: ~Tet(a) -> Dodec(e) Anyone have a clue on where to start with this?
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1answer
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How to solve the derivation?

Derive the following without assumptions: ¬∃xFx↔∀x¬Fx How do I solve this derivation?
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Completeness/Soundess of Second Order Logic

I recently read that Gödel's incompleteness theorem entails that second order logic cannot simultaneously hold the traits of: (i) completeness, (ii) soundness, and (iii) effectiveness. However, I saw ...
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2answers
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How does one prove ‘(B→C)→¬A’ from ‘(A→B)∨C’ and ‘(A→¬C)’ in Fitch?

I am trying to work my way through this Fitch proof, and I am not sure what I am doing wrong, but I keep getting stuck no matter what I try. First attempt: Second attempt:
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0answers
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Recommendation: Second Order Logic textbook

I'm looking into Universalist Realism, Nominalism, Trope theory and the application of Second Order logic to each of them, however I have little/no experience with Second Order logic. Please let me ...
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2answers
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How to get proof using proof editor and checker

How can I use http://proofs.openlogicproject.org/ or http://logic.tamu.edu/daemon.html to derive the given conclusion from the given premise: (∃x) ( Fx ∙ (y) (Fy → y = x) ) / (∃x) (y) (Fy ≡ y =...
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2answers
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How do you prove B v A |- A v B?

I am having trouble with how to use the assumption, which I feel that I will need for this proof. If any one can demonstrate or give hints for this proof, I would greatly appreciate it.
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3answers
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McGee's Counterexample to Modus Ponens

I'd like to start off by saying that I have read the other posts in the Math StackExchange and here about this paper, but I think my question is a bit different from those although it does stem from ...
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2answers
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Are Statements with Existential Quantifiers General or Particular?

Consider the following argument: The number 2 is a prime number and is divisible by 2. Thus, some prime number is divisible by 2. The first statement in this argument concerns a particular, i.e. ...
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How did Fitch's opposition to the Russell-Whitehead theory of types turn out since the 1950's?

In a footnote to Appendix C of Frederic Fitch's Symbolic Logic (page 217), Fitch writes about his article, "Self-Reference in Philosophy": It is reprinted here in order to indicate more fully my ...
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2answers
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How to prove ~ (~P & ~Q) : P ∨ Q by natural deduction

Here's another of Tomassi's exercises I can't solve (Logic, page 106): ~ (~P & ~Q) : P ∨ Q I have to use natural deduction and the only rules I know are: assumptions, modus ponendo ponens, ...
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234 views

2 simple Formal Fitch Proofs

I'm having difficulty proving these. They seem obvious, but I can't figure how to set up formal proofs for them. Could anyone give me clues on how to start them? ¬(P∧¬Q) from the premise P→Q; ¬Q→(R→P)...
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What is an example of a monadic predicate calculus argument that cannot be represented by the 19 classical Aristotelian syllogisms alone?

While reading Wikipedia's description of the monadic predicate calculus, I read the following: Inferences in term logic can all be represented in the monadic predicate calculus. and Conversely, ...
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0answers
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Proof from tree to steps

I'm able to get the proof in a tree form (it's invalid). Is there a method where I can transform it to steps method indicating the rules of inference and replacement?
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meaning of (r .⊃. s ⊃ r) [the syntax meaning]

I'm trying to to determine whether the following is a tautology, contingency, or contradictory: (p ⊃ q) ∨ (q ⊃ p) .⊃. (r .⊃. s ⊃ r) This is school work. I'm getting that it's a tautology, but only ...
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1answer
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Does this symbolic logic proof work?

So, I have this proof: Let a be an open sentential variable. Let K and C be prepositional variables asserted of sentences. Given K(a) <=> C(a) & a C(a) <=> C( C(a)) C(a & b) <=> C(...
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1answer
84 views

Prove transitivity in Fitch

How to prove transitivity in Fitch. Is it Ok? | 1. a = b | 2. b = c | 3. c = c =Intro | 4. a = c =Elim: 3, 2 | 5. b = c =Elim: 4, 1
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1answer
104 views

Derive |- [(P>Q)>P]>P using only primitive rules

I've been having issues trying to derive |- [(P>Q)>P]>P in natural deduction using only primitive rules. Wondering if anyone would have a solution to it. Thanks
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1answer
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Logic Either..Or

In the book: "Elementary Logic" authored by Brian Garrett, he has a few examples, one with solution and one without that conclude the following: 1) Either many people will attend the concert, or it ...
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2answers
80 views

~(P&Q) derive to ~Pv~Q

I would be grateful if someone could derive, by showing the proofs that: ~(P&Q) derives to ~Pv~Q. The same derivation would be appreciated for |- [(P>Q)>P]>P
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2answers
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Is it possible to define argument validity as a formula?

Let A, B and C be propositions. Define ARG(A, B, C) as the following argument: A. B. Therefore, C. My goal is to create a formula whose truth value is equivalent to "ARG(A, B, C) is ...
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3answers
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How to prove P ∨ Q : ~ (~P & ~Q) with natural deduction

Here's another Tomassi's problem I can't solve (Logic, Exercise 3.9.1.17, page 106): P ∨ Q : ~ (~P & ~Q) I have to use natural deduction and the only rules I know are: assumptions, modus ...
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1answer
90 views

Could someone help me prove (P → Q) ↔ (~P ∨ Q) follows from (P ∨ Q) ↔ (~P → Q) in sentential logic?

I need to prove that (P → Q) ↔ (~P ∨ Q) follows from (P ∨ Q) ↔ (~P → Q).
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3answers
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Is the reiteration rule in formal logic begging the question?

Wikipedia defines "begging the question" as To "beg the question" is to put forward an argument whose validity requires that its own conclusion is true. I assume this is something Aristotle's ...
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1answer
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How to prove ¬(p→q) ⊢ p &¬q

This is the first time I have posted anything on this forum. I am using Tomassi's Logic. Unfortunately I have been unable to solve some of the problems. One I can't solve is this one: ¬(p → q) ⊢ p &...
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2answers
186 views

Can inductive arguments be made in first order logic and, if not, why not?

After reading a question by rus9384 Why is faulty generalization called an informal fallacy? I wondered whether induction can be part of any argument in first order logic (FOL). rus9384 symbolized ...
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How to show that (P & Q) v (~P v ~ Q) is a theorem in SD

I’m working on a practice question on my logic textbook. And I’m stuck at this question. This is what I have so far: 1. ~(P & Q) Assumption/ Negated Eelimination 2. P Assumption/...
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1answer
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Need help translating a formal definition into FOL

I need help formally translating the following definition into FOL: "a property F is essential to an object x if and only if x could not have been the object it is without possessing the property F." ...
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1answer
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Predicate Logic - Universal Introduction

Another question I'm struggling on with predicate logic: Premises: (There exists x) ~Fx (For all x) Ox Desired conclusion: ~(For all x)(Ox > Fx) (if Ox, then Fx) My thoughts are to start by ...
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1answer
52 views

Predicate Logic - Existential Elimination

I am working on a predicate logic proof given the following premises: (For all x)(Fx > Vx) (There exists x)(Fx & Bx) Desired conclusion: (There exists) (Vx & Bx) My instinct here says to ...
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3answers
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Symbolic Logic - Negation Introduction

I am working on a problem for an online class that I'm struggling to figure out. I'm given these premises: 1. (H > (A > B)) (The > sign here represents conditional) 2. (~K & ~B) 3. (~A > K) The ...
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1answer
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Monadic Predicate and Polyadic Predicate?

Consider the following sentences; how would each be symbolized?: "Kate loves John" vs. "Kate loves cheese" ^(here, I'm trying to understand the difference between a relation between two individuals ...
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3answers
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“Kids shout at plants” (relation vs implication?)

I suspect "Kids shout at plants" can be represented as an implication: (x)(y)[Kx --> (Py --> Sx)] or as a relation Skp Is this correct? Why or why not?
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1answer
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Applying rules of inference in natural deduction

When applying a rule of inference, is it okay to "skip" a step (i.e, apply a same rule to multiple parts of a statement)? For example: (A > B) ^ (C > D) (~A v B) ^ (~C v D) 1, Impl. As opposed ...
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Step by step natural deduction: (T > E) ^ (A > L) /… (T v A) > (E v L)

I'm having trouble proving the following using natural deduction: (T > E) ^ (A > L) /... (T v A) > (E v L) I checked the answer but I didn't quite understanding the reason why the proof progressed ...
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How do I prove: 1. A v (B & C) 2. (A v C) > ~(G & O) / ~G v ~O

This is a question for my philosophy. Prove this valid using any of the rules we've studied so far: A v (B & C) (A v C) > ~(G & O) / ~G v ~O
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Do mathematicians take Modern Logic to be an appropriate representation of our sense of logic?

What examples do we have of mathematicians who explicitly and publicly expressed their personal confidence that mainstream modern logic, as used in mathematics, either as object of study in itself or ...
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1answer
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What is the proof for the Reductio (in a derivation)

In deductive logic, we may make the following step: ( {Γ,P}⊨Q & {Γ,P}⊨¬Q ) ⇒ {Γ}⊨¬P I've been trying to find examples of a proof that this inference follows, but I've struggled with my search. ...
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1answer
483 views

What, at present, are the major unsolved problems of logic?

In the 1900s, Hilbert published a list of 23 (later 24) unsolved problems in mathematics, which sparked increased research into each of them and the subsequent resolution of several of these problems. ...
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Formalizing negations

I'm working through a problem now that asks whether it is possible to logically formalize two sentences: "Say of each of the following pairs of English sentences whether there is a sentence φ of L1 ...
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Is the Completeness of a logical system considered an integral part any 'good' logical system?

Most logical systems will have two distinct forms of entailment, one is system-based entailment (logical consequence), and the other is proof-based entailment (derivability). In the former, an ...