Logic is the study of formal systems of reasoning, especially of the deductive variety. It is one of the few fundamental philosophical subdisciplines, along with metaphysics, ontology and aesthetics. Logic has taken on considerable importance in recent mathematical developments, and one of the ...

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Are there any strong reasons to still consider logical monism or a “One True Logic” in light of all the non-classical logics that have been developed?

I know there has always been some debate concerning whether or not a certain logical system (like classical logic) is the correct one, especially when it comes to propositional claims about the ...
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63 views

Formalism: philosophy of mathematics

Is it a contradiction, if I am a formalist but I think that mathematical objects are created by human mind ? In other words: Am I allowed to be a formalist and to believe that ...
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58 views

What form of formalist am I?

I am an formalist in the sense that I think that mathematics is just manipulation of symbols. But I think that this manipulation is motivated by the phantasy of humans: mathematical objects are for me ...
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123 views

Law of excluded middle: mathematical philosophy

Is it a contradiction, if mathematical objects are for me "mental constructions" -- like in intuitionism but I accept classical mathematics and the Law oft excluded middle ?
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53 views

The validity of the definition of a valid argument

I have some serious problems understanding what counts as a valid argument and what does not. I have read some different definitions of what a valid argument is: An argument is valid if (1.) The ...
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55 views

Law of excluded middle in intuitionistic formalism

Does intuitionistic formalism accept the law of exluded middle?
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86 views

Should we make ourselves clear in arguments?

Let's say there's the claim: There is a place that men are forbidden to enter. I think we are allowed to say that ginger-haired men mustn't enter there. But are we allowed to say that there is ...
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66 views

Mathematical philosophy: intuitionistic formalism

What is intuitionistic formalism? Tarski called himself an intuitionistic formalist.
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590 views

What practical methods can be used to prove a negative claim?

I realize that the burden of proof falls squarely on the shoulders of the person making the claim, but they often seem unwilling to do the footwork. It is difficult to prove a negative case except by ...
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62 views

Mathematical logic question from Rosen book

I am working through the Rosen Discrete Mathematics book. The question is; M(x,y) = x has sent y an email message Use quantifiers to express; There are 2 students in your class who have sent each ...
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21 views

FOL – Quantifiers and prenex form (from LPL 11.37)

Prenex form – when all the quantifiers are at the front I am struggling to figure out a couple questions from my book: #7 – ∃x [Cube(x) → ∀x Small(x)] #8 – ∃x [Cube(x) → ∀x Cube(x)] I never came ...
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42 views

Physical Age vs Mental Age [closed]

A 25 year old woman looks 15 years old vs a 15 year old looks like a 25 year old. If someone is attracted to a 25 year old woman but she looks 15, does that make him a pedophile? And alternatively, ...
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34 views

What's the difference (if any) between demonstration and description?

How do philosophers of various schools* explain the difference (if any) between demonstration and mere description? Are they synonymous, or are they different? How so? My first impressions: To ...
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What's the name for this kind of argument: This book or this person says P is true, therefore P must be true

People often claim P is true because a single book or person says P is true. This is most often the case when the book or the person is said to be divine. So is it a fallacy when people theorise the ...
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1. “X is a subset or part of y. x is true. so, y is true.” 2. “x came from y. y is true. so x is true”. Which fallacy are they?

example of the second argument. 'ad-duniya' (an arabic word) means 'nearer'. the word is denoted 115 times in Quran. In some cases the word 'ad-duniya' has been used for the meaning 'this world'. So ...
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46 views

“Change” last forever? If not what fallacy breaks the chain of reasoning shown here?

In movies, a frequently mentioned idea is that "Nothing lasts forever" .There's also a Chinese saying 變幻是永恆 Having thought too much into treating concepts as something similar to "building blocks", I ...
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40 views

Does this sacrifice dilemma has a name and has been studied by anyone?

The dilemma is the following. There's a button, if you press it, the world will get fixed by curing aids, cancer, fixing world hunger, homelessness, etc. HOWEVER You will die in 6 hours and receive no ...
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71 views

If V, then W. If W and X, then Y or Z. Not Y. Not Z. How to deduce the conclusion?

Prescript: I quoted the standard form of argument because its use of colours improves readability. Source: 6 minutes 01 seconds juncture; Lecture 13, Video 5 (transcription inexistent); MITx: 24.00x ...
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123 views

Would two identical people ever be able to communicate successfully?

Let's say you know some guy. And you told him that he was going to be copied and both him and the clone moved to an area where there are no external factors. After telling the man this, the man is ...
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5answers
146 views

Do humans make decisions based on logic or emotions?

I often hear that we are emotional beings, that we make decisions based on our feelings, mood and emotions. These decisions may not be logical and serve us best. On the other hand some argue that we ...
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64 views

LPL 10.26 - Fitch - How to use ∀ Intro and ∃ Elim?

I am using LPL (Language, Proof, and Logic, commonly known as LPL) and the bundled Fitch program. I am trying to solve problem 10.26: 10.26: ∀x Tet(b) ↔ ∃w Tet(b) Looks simple enough, as the ...
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59 views

Looking for references for some remark of Quine's

I'm looking for a comment I think I remember Quine having made. He's talking about our understanding of proofs. I think he says something along the following lines... If you understand many different ...
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88 views

Can the “accident” fallacy be applied to religious laws?

I need help understanding a discussion of the accident fallacy from the following site: http://www.logicallyfallacious.com/index.php/logical-fallacies/2-accident-fallacy It describes the following as ...
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71 views

Why is Tarski's notion of logical validity preferred to deductive one?

Its flaws are well-known and serious. To recall, an inference from A to B is valid iff all interpretations of "non-logical constants" that make A true also make B true. What are interpretations, ...
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83 views

An invalid argument, the conclusion of which is a tautology

Why it is not possible to have such argument? I found some textbook Introduction to Formal Logic and this is from one of the first excercises. This is marked as impossible, but I do not understand ...
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59 views

What is the relation between a conditional sentence and the corresponding universal statement?

I had a technical question about conditionals. To use an example, consider the following conditional statement, (1) If X is a man, then X is a father I consider (1) to be false because I consider ...
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When an individual makes a discovery

When an individual, or society as a whole, makes a discovery, different outcomes can occur e.g., they can enrich the individual or, they can debilitate the individual or, they can confront the ...
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33 views

When a fallacy actually occurs

Assume a debate has occurred and a result ended the debate, but in this result a slippery slope is coming true - more specifically the contrapositive used as a basis for argument that relied on a ...
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77 views

Argument against democracy/socialism as an ethical system [closed]

If n=4 people showed up and told you, "we're going to take our combined wages and vote about what to do with half of it", most people would consider it theft at best. Even in theory, I can't imagine ...
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101 views

Handling “paradoxes” in logic: The sentence after this is true. The sentence before this is false

My favorite paradox that leads to an endless regress, and also leads to a question: The sentence after this is true. The sentence before this is false When contradictions appear in proofs, ...
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28 views

“Don't do what I tell you not to do” - what to do if you always do the opposite? [duplicate]

I'm not sure if philosophy is the right topic for this, but it's logic and language, so it kind of matches. Me and my friend played a little game this morning where I said "don't do this and that" ...
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176 views

What are the important effects of studying logic?

I'm working on my assignment in Logic and I'm having a hard time answering this question maybe because my insights about the subject isn't enough because we're just getting started, So can you please ...
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161 views

How does infinity of numbers and of space work?

Is infinity just continuous generation of numbers, or can space be actually infinite? If it is finite can we see it expand if we went to the edge? When I say "I am counting to infinity" does it mean ...
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123 views

How to interpret “it is possible that x is impossible”?

The question is about the logical form of the sentence, x can be any object or process, actual infinity, tachyon, philosophical zombie, telepathy, etc. To conclude that x is impossible we are supposed ...
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62 views

What is the term used for logic statements which are non reversible?

Something along the lines of If A then B, if B then not. A has to be true before B can be true but if B is true first then A isn't true. Is there a term describing this in logic or philosophy?
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40 views

What is the connection between temporal and epistemic knowledge?

Recently I read all kinds of work from logic scientists in which epistemic logic was the main topic. Where epistmic change refers to change in knowledge of some agent in a multi-agent system (in a ...
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109 views

Why Continue Using Logic Symbology and Truth Tables

With the advent of computers and the creation and adoption of so many computer programming languages, are logic symbols still valuable or are they a relic of the past? If logic symbology remains ...
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68 views

What is the “simple logical truth” that makes omniscience self-contradictory?

Patrick Grim claims in "Problems with Omniscience" that there is a "simple truth well established as a logical theorem", which shows that omniscience is a contradictory concept. I am failing to see ...
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58 views

Does “the experience of transition requires negotiation between sacrifice and opportunity” make sense logically? [closed]

I've thought about this statement enough to know it doesn't make logical sense, but I've not thought hard enough to determine why it doesn't make logical sense. The word 'and' conceptually links two ...
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347 views

Is Socrates wrong in 'Euthyphro'?

I'm trying to understand 'Euthyphro', a popular book by Plato about Socrates. I believe I'm understanding what Socrates is saying; however I do not think it is correct. Referring to 10d to 11b ...
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93 views

Logical sentence… or not?

The following sentence, which is part of a presentation of the doctrine of structural holism and is translated from the french, does not seem quite to make sense to me: "each one [of the members of a ...
2
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1answer
59 views

Is there a suppressed premise in Anselm's Ontological Argument?

Source: 5 minutes 20 seconds juncture; Lecture 1, Video 4 (transcription); MITx: 24.00x Introduction to Philosophy; by MIT Associate Prof Caspar Hare PhD (Princeton) [...] Suppose God existed in ...
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54 views

Interpretation of implication symbol in modal logic

Suppose we have two propositions p and q, and an implication of this form: p → □q I can think of two potential interpretations of the meaning of this in terms of possible worlds: If p is true in ...
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92 views

Definition of “proof”

I read a book of logical puzzles once and there was a little story in it (fictional) about some boy who received an F on his geometry test because his professor said his proof that all angles of a ...
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137 views

Argument infinite regression problem about “why we should go vegan”

It should be familiar that some groups, particularly animal rights groups have always been trying to pursue others to go vegan One of the argument goes like this: "Animals want to live, and they ...
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87 views

How to deal with counterfactuals with false antecedents

Consider the following hypothetical question: If there were two moons, what kind of poem would be composed? There are two ways of considering this type of statement that I find unexciting: Any ...
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“None of the tall people are rich. Joe is rich, therefore Joe isn't tall.” Is this valid?

I've thought about it into two ways but I don't know if either, neither or bow are correct: First using sets: Given the sets "T" (tall people) y "R"(rich people), for Joe to be tall and rich, Joe has ...
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125 views

How to define a number [closed]

What is the positive real number (say less than one) that is not a rational nor an irrational number? I have encountered a mathematical problem that confused me about the definition of real ...
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61 views

Symbol to denote a credulous consequence

I have been trying to find the correct symbol to denote a credulous consequence. I've only been successful in finding the symbol for skeptical consequence, does a symbol for credulous consequence ...
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33 views

A form of appealing to nature?

I'm wondering if you could say that this is a from of the Natural fallacy: Example 1: Evolution has made us omnivorous, therefore eating meat is correct. Example 2: Animals eat animals, I'm an ...