Questions tagged [logic]

For questions about logic, whether it concerns syllogistic logic, mathematical logic or the nature of logic itself.

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56
votes
21answers
14k views

Is the “omniscient-omnipotent-omnipresent” definition of God consistent?

God is commonly defined as an omniscient (infinite knowledge), omnipotent (unlimited power), omnipresent (present everywhere) entity. Is there any logical inconsistency in this definition? I have ...
20
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1answer
12k views

How can we reason about “if P then Q” or “P only if Q” statements in propositional logic?

When you have a propositional sentence of the form P ⊃ Q  — which we might read as "if P, then Q" — how can you tell when it is true, or false, based on the truth-values of P and ...
27
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9answers
203k views

What is the difference between Fact and Truth?

I'm curious about the difference between Fact and Truth. I was searching on the internet if I could find it. But still I'm confused about the exact meaning. I first read the forum discussion here Fact ...
63
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12answers
15k views

Can you prove anything in philosophy?

I don't understand philosophy very well, and so I am wondering whether you can "prove" anything in philosophy. It always seems you can go a layer down, and find another question, almost endlessly ...
33
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13answers
5k views

What are the necessary conditions for an action to be regarded as a free choice?

A common philosophical question revolves around the existence of free will, but what I've found is that these debates seem to gloss over the concept of "free will" itself, either taking it as a given ...
19
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7answers
16k views

Is infinite regress of causation possible? Is infinite regress of causation necessary?

For a number of reasons — including perhaps a desire to feel that we have a complete understanding of where we came from, or at least an understanding which is completely sufficient for all of ...
16
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2answers
16k views

What fallacy dismisses problems by presenting “bigger” problems?

Wasn't really sure how to phrase this, but I'm thinking of an instance in which someone diminishes a problem by presenting one of larger scope - as a rather shoddy example, "x political problem in ...
40
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15answers
14k views

Does a negative claimant have a burden of proof?

I have often heard it said that the burden of proof is on the positive claimant but not on the one making a negative claim. A person claiming, "God exists" has a burden of proof but not a person ...
15
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6answers
4k views

Is God either immoral or not omnipotent?

The usual (Christian) justification for suffering/evil in the world created by a benevolent God is freedom of the will. However, the more interesting question is not about the source of evil (which ...
9
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2answers
6k views

What are the more complex/interesting examples of synthetic a priori statements?

The usual examples of synthetic a priori statements are – it seems at least since Kant: "Nothing can be simultaneously red and green all over" 7 + 5 = 12 (or any other basic arithmetic statements). ...
6
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12answers
16k views

Is it possible to know anything with certainty?

I have been thinking about objectivism vs relativism recently. It is easy to prove by contradiction that there exist objective truths. However, is it possible to know anything? If you assume a human ...
39
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16answers
10k views

How to get started with philosophy without getting overwhelmed quickly?

I’ve spent a lot of time trying to find how to get started with philosophy but I can’t. It seems that getting started with computer programming is nothing in comparison - with computer programming it’...
6
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2answers
729 views

What are the differences between philosophies presupposing one Logic versus many logics?

I was wondering in light of the historical developments of logic since ancient Greeks and well into the nineteenth and twentieth centuries: What kind of a philosophy assumes only one Logic, and what ...
11
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4answers
4k views

How do I check if two logical expressions are equivalent?

For example: Is (A ∨ B ∨ C) ∧ (D ∨ E ∨ F) the same as (A ∧ D) ∨ (A ∧ E) ∨ (A ∧ F) ∨ (B ∧ D) ∨ (B ∧ E) ∨ ( B ∧ F) ∨ (C ∧ D) ∨ (C &...
4
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4answers
1k views

What is the logical form of the definition of validity?

My text book gives the definition of validity as "An argument is valid IFF if the premises are true, then the conclusion must be true". Using a conditional elimination on the RHS of the IFF yields "An ...
19
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8answers
27k views

What is the difference between “necessary” and “sufficient”?

What is the logical difference between something being necessary in order for something else to be true; as opposed to something being sufficient to make something else true. i.e. Fuel is sufficient ...
11
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3answers
463 views

Do all epistemologies suffer from the “regress of justifications” problem?

Aristotle describes the regress problem in his logical work Posterior Analytics I.2: b5. Some hold that, owing to the necessity of knowing the primary premisses, there is no scientific knowledge. ...
7
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2answers
378 views

Does Tegmark's Mathematical Universe hypothesis allow existence of alternative mathematics?

Tegmark's mathematical multiverse hypothesis assumes that all mathematical structures exist as universes But do you know whether his hypothesis also allows/accept universes described by other types ...
3
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6answers
612 views

Is the use of inconsistent definitions a logical fallacy?

I am not asking for a defense of or pro/con of the existence of an omnipotent (or multiple omni-x) being, or for the existence of square-circles or any other similar thing. These arguments are well ...
7
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3answers
668 views

Is there modal logic without possible worlds?

Would it be desirable to carry out a deflationary research programme in modal logic? In other words, would it be desirable to re-think modal logic without the possible worlds semantics? The original ...
6
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5answers
779 views

What fallacy dismisses a conclusion because supporters give invalid arguments for it?

A person dismisses an otherwise valid argument, because some of its proponents support it for the wrong reason. How is this fallacy called? EDIT: Here is an example. A person defends the idea that ...
4
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6answers
2k views

Can logic be used to prove any belief?

I have witnessed a lot of debates and arguments of different beliefs, and noticed that each side uses logic to prove its point. So, can any belief be proven by logic regardless of its nature (...
19
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7answers
2k views

What formal logical systems “resolve” the Liar Paradox?

Short version of my question. What formal logical systems can represent, and seem robust against, the Liar Paradox? N.B. I would like to avoid reference to truth-values, except inasmuch as they ...
12
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2answers
2k views

What is the philosophical ground for distinguishing logic and mathematics?

I was wondering why the field of mathematics and that of logic are perceived as two distinct fields. Although could be pleased with the intuition that logic is rather meta-mathematics, still would ...
8
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2answers
583 views

Existential import: in logic, do propositions default to true or false when objects in them do not exist?

In this hypothetical: Firefighters always tell the truth, while politicians always tell lies. Suppose three people, who are either a mix of firefighters and politicians, all politicians, or all ...
6
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2answers
379 views

Are arguments based on conceivability refuted by ideas from fantasy and sci-fi?

There are several arguments in metaphysics which are based on "conceivability": The ontological argument for God's existence. Hilary Putnam's Twin Earth argument for semantic externalism (the idea ...
3
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1answer
421 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 ...
10
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9answers
2k views

How can we justify the use of logic?

I would like to hear some philosophical arguments which justify the use of logic. Additionally, if a justification of logic takes the form of an inference, is it a problem if this inference itself ...
21
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12answers
2k views

Motivations for dialetheism?

At the request of the moderators, I've reformulated this question to change the emphasis of the question to something perhaps a little more broad-ranging: Question. What are the major modern ...
6
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3answers
560 views

Is free will a third option aside from chance and necessity?

The determinism dilemma is that if our actions are predetermined they are not free, and if they are random they are not willed, either way there is no free will. Even if will causation is a mixture of ...
5
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5answers
2k views

Why are conditionals with false antecedents considered true?

I don't understand what conceptual sense this scenario makes, or what the motivation behind the decision to make conditionals with a false antecedent true was. Can anyone help me understand this? ...
12
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2answers
377 views

Was Locke right that analytic knowledge is vacuous?

According to Locke, it is impossible to obtain substantive knowledge from analytic propositions. Statements like "triangle has three sides" are analytic, but one cannot derive the Pythagorean Theorem ...
7
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3answers
443 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, a.k.a....
4
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4answers
850 views

How does Plantinga's free will defense of God's benevolence work?

The purpose of the defense is to show that omniscient, omnipotent and benevolent God is consistent with the existence of evil in creation. The most popular version of the defense is due to Alvin ...
14
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2answers
824 views

What are the current topics in philosophy of logic?

I'm contemplating another attempt at completing my long delayed MA in Philosophy, and I need a new thesis topic. As a student I excelled in advanced symbolic logic, but my connection with academic ...
3
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2answers
847 views

Can paraconsistent or other logics make the impossible happen?

A paraconsistent logic system it is defined as "a logical system that attempts to deal with contradictions in a discriminating way. Alternatively, paraconsistent logic is the subfield of logic that ...
4
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8answers
394 views

Intuitively, why does (B → S) ≡ (¬B ∨ S)?

I pursue only intuition; please do not answer with formal proofs or Truth Tables. I comprehend the following explanation, but it still does not supply the intuition and I sense a deeper, directer, ...
161
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15answers
43k views

Is 'guns don't kill people, people kill people' a good argument?

I'm hearing the argument X doesn't do Y people do Y in quite a few guises. For instance in it's original form guns don't kill people; people kill people Presumably, therefore guns are OK cars ...
15
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7answers
2k views

Is Logic Empirical?

We use the logical system that we know from observations (empirical data) holds true in the world we live in (please correct me if I am wrong). Hence the axioms of logic we choose are themselves ...
4
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4answers
995 views

Is logic subjective?

If logic is constructed from axioms, and axioms are depended on observation which in term could be subjective, does this means that logic could be limited to our observation, and not really absolute ...
7
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3answers
1k views

Where is a good place to start reading about logic?

I would like to learn logic as an introductory subject. I am an undergraduate student and would appreciate any suggestions for books/articles where I can start from, also any books/articles about ...
6
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5answers
1k views

How does actual infinity (of numbers or 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 ...
9
votes
1answer
242 views

What is the difference between depth and surface information?

I was looking for an answer to this question: Was Euclid's method of proof axiomatic? While doing so I ran across an abstract of Jaakko Hintikka for an article "What is the axiomatic method?" ...
7
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2answers
850 views

What is the relation between the material conditional in logic and conditionals that we use every day?

The material conditional has a truth-value of T in every case except where the antecedent proposition is true and the consequent is false. However, this means that many conditionals are true (if only ...
4
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4answers
1k views

Validity of an argument with a contradictory conclusion [duplicate]

I have an argument with the conclusion: 'The sky is blue and it is not the case that the sky is blue'. Without knowing the premises of this argument, am I right in saying this argument is invalid ...
1
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2answers
330 views

References for the justification of the use of Logic

Following that question : How to justify the use of logic? I'm looking for references of the justification of the use of Logic (the question above didn't ask explicitly for resources but rather for a ...
2
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4answers
215 views

Why do we need Aristotle's theory of predication?

My question is about Aristotle's theory of predication. Why do we need it at all? I know it's intuitive to pick up something and say something about it like "S is P", but doesn't this lead us to ...
1
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3answers
627 views

Deduction vs Induction — are they equally valid?

I've been reading on deduction vs induction as two primary modes of reasoning. Can't exactly remember where but I have also seen deduction being described as backward and induction as forward thinking....
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3answers
1k views

Why do we take deductive and inductive reasoning for granted?

In philosophy, we doubt everything, even the things which seem obvious and intuitive. So why do we accept deductive and inductive reasoning without doubting their validity?
24
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4answers
4k views

What are the philosophical implications of category theory?

I have heard about topoi being the ideal entities to use for foundations of mathematics (since we are able to reasonably interpret our theories in them), so I imagine there might possibly be some ...