Tagged Questions

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 ...

learn more… | top users | synonyms (2)

10
votes
8answers
843 views

Philosophy books for a smart 9 year old

I would like to buy some books on philosophy for the child of a friend. He is very mathematical able and clever and nine years old. I remember near that age really enjoying the idea of logic (in ...
0
votes
1answer
34 views

Simple Predicate Logic Questions (transcription and interpretation)

Taking an introductory logic course and we're currently transitioning from sentence logic to predicate logic. It's not really clicking for me just yet. There are 2 specific questions from the textbook ...
1
vote
2answers
38 views

Can deontic conditionals be indicative?

To check my understanding, the following is an indicative deontic conditional, correct? "If you live in Texas, you ought to watch football." It is indicative in the sense that it is reporting on ...
-2
votes
0answers
12 views

What's 'external logic'? [on hold]

Source: p 96, The Law of Contract, 5 ed (2012), by O’Sullivan and Hilliard Bilateral contract made before it is due to be performed, as where A and B make a contract in January for the ...
-1
votes
1answer
48 views

Why happiness is induced by that which baffles us: What does laughter reveals about human nature? [closed]

I will attempt to be prompt. Variables/strings/operators: *The prime symbol (') will be used as an operator for an action's derivative [here, meaning antecedent] (e.g (eating a sandwich)' = ...
-1
votes
1answer
34 views

Propositional Logic - Best Way to Translate Complex Legal Statutes

If one wanted to use standard propositional logic, what would be the most efficient way to translate a sentence from a natural language like: "Capital murder is the premeditated or non-premeditated ...
0
votes
1answer
33 views

birds of a feather flock together and guit by association

There is a saying "birds of a feather flock together" which usually boils down to People of similar character, background, or taste tend to congregate or associate with one another. Yet guilt by ...
1
vote
3answers
75 views

An argument is valid if the premises CANNOT all be true without the conclusion being true as well

"An argument is valid if the premises CANNOT all be true without the conclusion being true as well." Argument_1: P or Q. not Q. Therefore, P. Argument_1 is valid. Argument_2: B or M. M or C. ...
1
vote
4answers
137 views

What does the statement “Xs exist” really mean?

If someone were to claim: Xs exist. what do they actually mean? Do they mean: At least one X exists. or At least two Xs exist. In other words, does the phrase "Unicorns exist" mean "at ...
1
vote
2answers
85 views

How to prove the axiom is wrong?

The father of math (Euclid) wrote a book named Elements. The book is full of axioms and here are some of them I am interested in: Things equal to the same thing are also equal to one another. ...
1
vote
1answer
120 views

How do I use the “Barbara, Celarent, … etc.” mnemonic?

Medieval logicians memorized this most famous logic mnemonic: Barbara, Celarent, Darii, Ferio ← direct first figure Baralipton, Celantes, Dabitis, Fapesmo, Frisesomorum ← indirect first figure ...
3
votes
1answer
41 views

What kind of conditional does Nozick use in his theory of knowledge?

Knowledge is traditionally defined as justified true belief: in order for S to know P, S must believe P, P must be true, and S must be justified in believing P. Now this definition has been ...
0
votes
1answer
54 views

The Fallacy of Contraposition for Counterfactuals?

Example: 1.If Boris had gone (to the party), then O would still have gone. 2. Therefore, if O had not gone, then B would not have gone. Analysis: Suppose B wanted to go , but stayed away ... ...
1
vote
1answer
24 views

When are Counterfactuals transitive?

Analysis: For brevity, define 'gone' = 'gone to the party'. In this scenario, while it is true that had P gone, then A would have gone, and it is true that if A would have gone, then M would ...
0
votes
2answers
43 views

'If P were true' vs 'If P is the case'

Counterfactuals have this form: If [S:] P were true, Q would be true. Material conditional: If [P:] P is the case, then Q is the case. Counterfactuals are not material conditionals! [Does ...
6
votes
4answers
231 views

Can a “real” paradox exist?

Given a statement, S: "S is not true." We arrive at a paradoxical solution whether or not we assume S to be true or false. Does this automatically imply that we have made an error in logic, ...
2
votes
1answer
57 views

How to start studying philosophical logic?

As I'm planing to study Philosophical logic, I've some important questions. For example, I wonder: 1-Should I start with the algebraic approach? Should I start with another approach?(which one?) 2- ...
2
votes
1answer
41 views

How to discharge an assumption?

I am proving the follow argument [(A ↔ B ) → C] ⊢ [ - ( A ^ B) V C ] Using the following set of rules I, ^E, vI, vE, →I, →E, ↔I, ↔E, --E, -I Here are my steps but I got to the point where I ...
1
vote
1answer
29 views

What are the names, or arguments of the atomic sentence “Max ate a cake” and “I ate a cake.”

What are the names, or arguments of the atomic sentence Max ate a cake and I ate a cake. ? First of all, "Max" is definitely a name. But is "cake" a name? And in the second sentence, is ...
2
votes
1answer
62 views

Logical Consequence and Tarski's World

I found this question in an old exam paper. I have no idea what is expected from a question like this. Consider the Tarski's world below. This world illustrates that ¬∃xTet(x) is NOT a logical ...
2
votes
1answer
76 views

Help with a proof for the following arguments

I want to proof the following argument from both sides using the following rules ^I, ^E, vI, vE, →I, →E, ↔I, ↔E, --E, -I Argument [(A ↔ B ) → C] ⊢ [ - ( A ^ B) V C ] Please let me know ...
1
vote
2answers
219 views

Is it possible to provide a proof of the following arguments?

G & ¬ H ¬ H ⇒ H Therefore, S & I Is it possible to prove the validity of this argument without having any information of S or I in the premises? H ...
2
votes
5answers
72 views

Question regarding sound argument [duplicate]

Sound argument is an argument which is both valid and it's premises are true. But my question is, why do we mention in the definition of the sound argument that "it's premises are true" when we've ...
1
vote
1answer
48 views

Proof validity methods other than truth tables

I have read or heard some time ago that truth tables cannot be used to validate arguments which involves the use of quantifiers i.e. in predicate or quantificational logic where you can find ...
2
votes
4answers
144 views

Must infinity involve repetitions?

Infinity for Nietzsche in at least one line of argument involves the eternal return; he refers to it in the Die fröhliche Wissenschaft and Also sprach Zarathustra; most completely in his Notes on the ...
1
vote
2answers
64 views

Method to derive conclusions

Suppose, you have been given the following assumptions: 1. (W ⊃ (F ∨ M)) 2. ~F 3. (M ⊃ A) In what way you can come up with conclusion from this? What kind of inferences rules can be used here? I ...
5
votes
6answers
2k views

Climate change statement - is there a logical fallacy here?

"97% of scientists agree that climate change is caused by humans - if 97% of scientists told you a plane was going to crash, would you get on it?" Arguments about the existence of climate change ...
0
votes
1answer
66 views

Did Wittgenstein say something about intuition for logic?

When one creates some logical content, like in programming, only naives think that this is a rational way of thinking. In fact, this is based on patterns and intuition. Did Wittgenstein say anything ...
1
vote
3answers
44 views

Introductory Natural Deduction Question

So I'm new to logic and taking an introductory logic course, and I'm really having trouble with these 2 questions: Using the system of Natural Deduction in the textbook, provide a derivation to ...
1
vote
3answers
68 views

What is the logical connectives of Then?

What is the Truth Table Analysis of the below argument? If a football is more demanding than tennis and John is good football player, then John can become a good tennis player.But if football is ...
3
votes
3answers
123 views

Understanding why Quine thinks certain belief sentences are meaningless

According to Quine, the following sentence is literally nonsense: ∃x (Ralph believes that x is a spy) Question: Exactly how does the sentence above devolve into non-sense according to Quine? ...
2
votes
3answers
142 views

How does one contradiction in argument makes the argument valid?

For any argument such as the following that we solve by "Proof by contradiction" method: (A v B) (A ⊃ C) (B ⊃ D) [ Therefore, (C v D) Assumption: ~(C v D) Therefore, ~C {from 4} Therefore, ~D {from ...
1
vote
3answers
153 views

Logic - 3 Cannibals Riddle Reduced to 2 Steps

From reddit Cannibals ambush a safari in the jungle and capture three men. The cannibals give the men a single chance to escape uneaten. The captives are lined up in order of height, and are tied to ...
3
votes
4answers
136 views

Invalid arguments with true premises and true conclusion [duplicate]

I'm am study some classical logic and I am having trouble with argument validity. I learned to think of validity as determined by the definition "If the premises are true, then the conclusion must be ...
2
votes
1answer
82 views

Is there a name for a “You benefited therefore you did it” fallacy?

When talking about conspiracies, you often hear things like group X benefited from event Y therefore group X must have caused event Y I'm sure everyone knows lots of examples: 9-11, ISIS, ...
1
vote
0answers
33 views

Does anyone know of any essays on Adam's Thesis and Deontic Conditionals?

I'm curious if anyone knows of any essays which concerns how deontic conditionals fit with Adam's Thesis. (Adam's Thesis is the idea that the probability of an indicative conditional A > C is equal ...
-1
votes
4answers
106 views

Why is the Kochsche Curve and programming so similiar? [closed]

I've question which I'm looking for longer time. The iteration process while a for loop > for statement in function_declaration: is looping over all instances and giving out one statement after ...
2
votes
1answer
56 views

Using natural deduction rules give a formal proof

With exams just around the corner I am really struggling with formal proofs. Using natural deduction rules give a formal proof of Q from the premises (¬P → Q)∧(R → ¬Q) ¬Q → ¬S ¬S → (R ∧ ¬P) So the ...
0
votes
2answers
59 views

Anyone can help me with natural deduction?

~(AvB) ㅡㅡㅡㅡ ~(BvA) I have to provide a derivation to establish validation of this argument. First of all, Can i first change ~(AvB) into ~A&~B by using de-morgans? And second is ...
1
vote
4answers
137 views

Does a beginning imply an ending? (In regards to the universe)

In regards to the universe if it said to have a start (Beginning) does that imply that it will have an end? Are beginning and ends implied when either ones is said to be true of a proposition or can ...
1
vote
1answer
39 views

How to stop thinking on reasoning? [closed]

I think I always think on the base of reasons and logically, but relations have problems with Reasons and Logic. Like if we Trust some one, we should do without demanding the explanations. is it a ...
3
votes
2answers
126 views

Where does Quine say logic should have no ontological presuppositions?

I'm sure I recall Quine saying in various places that one distinction between logic and set theory is that logic should have no ontological presuppositions (or, at most should presuppose some thing ...
0
votes
1answer
60 views

Modus Ponens and Modus Tollens Symbolic Proofs

I need a symbolic step by step proof to show me the validity of Modus Ponens and Modus Tollens. And someone please define the validity of a particular argument for me, because as I know, the valid ...
2
votes
4answers
97 views

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 ...
3
votes
2answers
147 views

How could it be that the following sentence is NOT a proposition?

Consider the sentence "It might be dark outside". Is this a proposition? What sorts of arguments could you make that this sentence isn't a proposition? Is it that it is making -- potentially -- a ...
1
vote
1answer
37 views

What does it mean to “conditionalize a probability distrubition”?

What does it mean to "conditionalize a probability distrubition"? In case relevant, I've been reading about "Adam's Thesis", and that's where this phrase has been thrown about.
1
vote
3answers
140 views

Conditional disjunction equivalence proof using FItch

Prove P v Q ⇔ ¬Q → P So far I have the obvious things... 1. P v Q _ | 2. ¬Q | _ | 3. | 4. | 5. | 6. | 7. | 8. P 9. ¬Q → P → Intro 2-8 I think the problem here is that I do not ...
0
votes
0answers
42 views

An logical expression and its meaning

I will use an example sentence from Russell, so let W represent the predicate “... authored Waverley “ then (x)(Wx → (y)(Wy → y=x)) would express the same thing as the sentence 'At most one person ...
2
votes
1answer
178 views

Are there any other branch of mathematical philosophy?

Are there any other branch of mathematical philosophy? I am refer to the mathematical logic, are there any other branch of mathematical philosophy? For example, philosophical graph theory would be ...
9
votes
10answers
406 views

How could our universe suddenly appear out of nothingness?

How could our universe suddenly appear out of nothingness? I understand that the big bang created all things but how could it when nothingness is purely the absence of everything?