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Questions tagged [philosophy-of-logic]

Philosophy of logic is a branch of philosophy concerned with investigating the nature, scope and role of logic.

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Did any logician object to the idea that if two contingent propositions are true, then they imply one another?

Both the following sentences are true: On January 22, 2020, the earth is orbiting the sun. On January 21, 2020, Trump was the 45th president of the United States of America. So did any ...
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In non-platonism, can undecidable statements have truth value?

Most sources I can find about Gödel's incompleteness theorems summarize the result as "there exist true arithmetical statements that have no proof." It seems coherent to say that there exist ...
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Is there a logic or philosophy system resistant to retroactive actions or time travel? [closed]

Retroactive means making a change to the past with effects in present. Time travel means replaying events till the specific outcome.
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Can/Do there exist any quantifiers other than “there exists” and “for all”?

I'm curious about why there are only the two logical quantifiers there exists and for all. Intuition and human language support the idea that these quantifiers make sense, but otherwise it seems ...
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Bibliography about non-mathematical applications of logic:

I have been recently playing with modal and temporal modal logics in the context of "organisms" (mostly after some study of entelechy in Aristotle and relatedly, some ideas of current biology). I have ...
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Justification for the paradigm of abductive reasoning

In Chance , Love and Logic, Peirce defines reasoning into two categories: analytic and non-analytic. All forms of reasoning have three fundamental components: rule, case, result. Analytic reasoning ...
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Which of common rules of inference are rejected on some philosophical grounds?

My question is: is there a mathematical or philosophical basis for rejecting any of the following rules of inference? If yes, then what is the argument for rejecting any of them? I am asking this ...
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Did logicists use mathematical entities (in their attempt) to reduce mathematics to logic?

Two concepts F,G are equinumerous if there exists a one-to-one correspondence between the objects that fall under F and G. Equinumerosity is one the most fundamental building blocks of Gottlob ...
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What are the eventual purposes of symbolic logic?

What is the teleology of logic? Every body of knowledge has to have a teleology for which it's designed. The body of knowledge in logic doesn't clearly have any teleology or any purpose to which it ...
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Using logic to do metalogical proofs? Is there a circularity problem here?

(1) If modus tollens were not correct, then I could have (P-->Q), ~Q and P. (2) But I cannot have (P--> Q) , ~Q and P. For, in that case, I would have (~P v Q) and ~Q and P; which means I would have ...
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What is the difference between 'accidental' and 'contingent'?

What is different between 'accidental' and 'contingent'? I thought that accidental contains intentional notation while Contingent does not. But there could be an intentional action that turns out to ...
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Rhetoric: How to frame redundancy in an argument as deficiency?

How can we categorize redundancy in an argument as deficiency? That is, weaken the argument because of its redundancy? Suppose X is an argument that boasts coherence and clarity, but it has various ...
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What counts as a logically necessarily true statement and what is not?

"If an existing population contains both mortal and immortal beings, some members of that population are not subject to death." Is this statement considered logically necessarily true? I personally ...
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Is a tree proof or natural deduction a semantic method of proof?

Peter Schroeder-Heister writes in an article on "Proof-Theoretic Semantics" the following: Proof-theoretic semantics is inherently inferential, as it is inferential activity which manifests itself ...
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Is Herbrand semantics a kind of term formalism?

Michael Genesereth and Eric Kao describe Herbrand semantics as follows: Herbrand semantics is an alternative semantics for First Order Logic based on truth assignments for ground sentences rather ...
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Did early Wittgenstein view mathematics as “sense-less” or “non-sensical”?

G. E. M Anscombe makes the following distinction between Wittgenstein's use of sense-less (sinnlos) and nonsense (unsinnig): (page 163) We must distinguish in the theory of the Tractatus between ...
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Although Russell's paradox has the virtue of simplicity, is it a distraction from other paradoxes of naive set theory?

Given that Russell's paradox exhibits a contradiction in naive set theory, the interpretation of the binary relation "∈" called "membership" (where the expression "x ∈ m" is pronounced as "x is an ...
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What philosophical axes did 19th century mathematicians have to grind?

Tim Button's presentation of set theory motivates the subject by providing a history of 19th century mathematics where the notion of limit allowed definitions of the derivative and continuity. These ...
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Do Aristotle's three laws of logic apply to statements about the future?

I have just read about Aristotle's Three Laws of Logic. I was wondering if statements such as "There is a chance of it raining in the next hour" can be evaluated using the three laws. Can you apply ...
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What's the difference between a second-order relation and a relation between objects?

I was reading an article in philosophy and found this: Some philosophers have denied that there is such a relation as identity. Thus Ludwig Wittgenstein writes (Tractatus 5.5301): "That ...
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Aristotle's Categories and Linguistics

I have actually two questions: What he calls substances or non-substances seem to me as, now what we call a matter of language. So what he calls substances could be seen as concrete nouns, and non-...
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What is an example of a true contradiction in a paraconsistent logic?

While reading the Wikipedia article on trivialism I noticed the following: In classical logic, trivialism is in direct violation of Aristotle's law of noncontradiction. In philosophy, trivialism is ...
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Is there any exception that proves or suggests that the law of non-contradiction does not always apply?

Is there any exception that proves or suggests that the law of non-contradiction does not always apply? I am thinking, because the law of non-contradiction is very similar to the law of excluded ...
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Is there a difference between equality and identity?

Is there any difference between equality and identity, or are they the same concept?
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Is there any exception that proves or suggests that the law of excluded middle does not always apply?

Is there any exception that proves or suggests that the law of the excluded middle does not always apply? I am wondering if this rule is an absolute truth that is always true in our world or in any ...
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Why are there two fundamental laws of logic?

We have the law of non-contradiction and the law of excluded middle, but looking at it, it seems that both of them are the same thing, or at least one of them logically implies the other. Is there a ...
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What paradoxes arise from quantifying over EVERYTHING?

This question is in context of the umbrella view of objects, that there exists a general category that everything falls under. Here are the quote and link that peaked my curiosity. Finally, note ...
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Is there a generally agreed upon solution to Bradley's Infinite Regress without appeal to Paraconsistent Logic?

I'm interested in Priest's solution using paraconsistent logic, but before I embark on that, I wanted to know if there was a generally agreed upon solution in more "classical" schools of thought. ...
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Who first proposed that A → (B ∧ ¬B) ⊢ ¬A was the principle of proof of some theorems?

The proof of various theorems are nowadays routinely described as "proof by contradiction". For example, the following theorems: https://en.wikipedia.org/wiki/Proof_by_contradiction The ...
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What are the problems with Tractatus?

Tractatus, in a way, says World isn't what is out there, but is the world you imagine. World is what you would tell another person when you will recount this world. (It is what you would 'know' of the ...
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What are some benefits of a second order logic?

I have read that a second-order logic can help one define equality by quantifying over all predicates such as what is done in the following definition: (x=y):⟺[∀P:P(x)⟺P(y)] By contrast a first-...
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If I said I had $100 when asked, but I actually had $200, would I be lying by omission? [closed]

If you had $200 cash on you right now, and I asked you if you had $100 on you, would the correct answer be yes (always/no matter what other conditions there are), no (always/no matter what other ...
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Question about conjunctions

Would this principle be true for conjunctions: For any proposition p, if p is a conjunction with at least three conjuncts, then there are more distinct conjunctions that can be created out of the ...
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Why is it argued that an argument has one and only one conclusion?

Why can't an argument have more than just one conclusion? If we assume some premises and we assume them to be true, then by some inference rules we are sometimes able to deduce more than just one true ...
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What is the difference in logic between strong and weak negation?

My main concern is to separate different forms of logic. I am hoping to use negation as a way to do that. In the abstract to "Web Rules Need Two Kinds of Negation", Gerd Wagner writes ... there ...
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Help with an existential natural deduction proof

From the assumption ∃x∃y R(x, y) I need to derive the conclusion ∃y∃x R(x, y) From the comments: I tried to use Existential Elimination but I can't figure out how to do it properly.
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How does one go about this natural deduction proof?

From no assumptions derive the conclusion ∃x t = x (where t can be any term).
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Decidability of predicate logic

In the language of predicate logic with only identity and no predicates, function symbols, or constants, is it possible to construct infinitely many non-equivalent formulas?
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How does Dummett see deductive inference extending our knowledge?

Michael Dummett writes (page 195) Once the justification of deductive inference is perceived as philosophically problematic at all, the temptation to which most philosophers succumb is to offer too ...
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How do we separate rules of logic from non-logical constraints?

I think that very often the idea of 'constraint' appears in mathematics. For example, when a triangle is considered, 3 points are constrained not to be co-linear, and then we try to discover the ...
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Book Introduction to Logic. Patrick Suppes-Section 2.1-Excercise 4

Anybody can help me with the solution of this exercise? Construct a (non valid) rule of inference which by itself will satisfy Criterion II but violates Criterion I? Thank you in advance. Diego.
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What exactly is a first-order logic?

Can someone explain in simple terms what exactly is a first-order logic? From my amateur standpoint, I think that first-order logic is a some kind of a system of symbols and general logical rules and ...
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The mechanics of logic [closed]

I am interested in how fundamentally important measurement is in the process of logical thought. At what point in the logical process are we no longer engaged in some form of measurement. Measurement ...
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Why are non-logical predicates of 0-arity treated as logical variables?

In the "Non-logical symbols" section of Wikipedia, it states: A predicate symbol (or relation symbol) with some valence (or arity, number of arguments) greater than or equal to 0. These are ...
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'Truth conditions cannot simultaneously serve as both a definition of truth and meaning of sentence' What does this mean?

I am reading Hintikka's article on logical consequence in Oxford handbook of Philosophy of math and logic, and he was talking about the meaings of logical constants, when the following excerpt ...
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Can classical logic have deduction with infinite steps

I've been reading the Stanford Encyclopedia of Philosophy article on classical logic, and I've been confused about Theorem 9, and the preceding statement. They mention how (*), the clause which ...
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Does any mathematician today work on a logic he explicitly presents as somehow true of human logic, as Boole did in his time?

Mathematicians make sure their theories are logically consistent but not necessarily that they are somehow true of anything in the real world. This may be compared with scientists whose research ...
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Understanding Hintikka's scandal of deduction (as depicted by D'Agostino)

I am having trouble understanding Hintikka's Scandal of Deduction, as depicted in D'Agostino's article. According to this account, the problem stems from the fact that, while first order logic is ...
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Do you know of any mathematical theorem whose proof relies on the use of the principle of explosion (ECQ)?

Ex contradictione (sequitur) quodlibet (ECQ) is almost universally recognised in mathematical logic as a valid inference. In symbolic logic, this inference is usually expressed in the following way: ...
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Can hypercomputation compute the impossible?

There are things which are illogical/logically impossible (like saying that 2+2=4 and 2+2=5. Without changing anything in the axioms of mathematics or logic, this would be a contradiction and would be ...