Podcast #128: We chat with Kent C Dodds about why he loves React and discuss what life was like in the dark days before Git. Listen now.

Questions tagged [logic]

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

Filter by
Sorted by
Tagged with
1
vote
1answer
222 views

Which is the difference between Sache and Sachverhalt in the Tractatus?

As far as I know, When Russell asked to Wittgenstein to tell him the difference between Sache and Sachverhalt, Wittgenstein answered that "Sachverhalt" is what corresponds to an elementar sätze (an ...
1
vote
1answer
362 views

Necessity in relation to possibility

(1) Does necessity (materially) imply possibility? (2) Does possibility (materially) imply necessity? From a logical point of view: If by material implication (A -> B), we mean (-A or B), then it ...
1
vote
2answers
940 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 ...
1
vote
2answers
2k views

How to prove a theorem using Sentential Derivation

I have to prove that [¬ A → ¬ (A → B)] → A is a theorem using the rules of SD. Any hints or advice?
1
vote
5answers
248 views

Is it irrational to take a risk?

When person A says to person B, "You're being irrational," is it fair for person A to mean the following? What you are doing is a bad choice! I know because your alternative is 75% likely to be ...
1
vote
3answers
122 views

A question about logic [closed]

Say person A concluded that when a king makes a statement to his people about X, the people will revolt. And person B concludes that if that king makes a statement to his people about X, the people ...
1
vote
1answer
151 views

Is a barber a barber if he doesn't get paid?

For reference: The Barber Paradox. The Barber is he who shaves all those, and only those, who doesn't shave themselves. Now the question is: Who shaves the Barber? The paradox being that if ...
1
vote
3answers
161 views

How do you decide how these Conditional Statements written in prose should be symbolised: (A → B) → C or A → (B → C)?

Even after rereading this, I still cannot distinguish intuitively (A → B) → C vs A → (B → C). So please allow me to concretise that question with this example (from scrolling 40% down here): [1.] ...
1
vote
2answers
270 views

Can a useful, formal system of logic be constructed with no axioms or assumptions, or perhaps using only Occam's razor?

Can a useful, formal system of logic be constructed with no axioms or assumptions, or perhaps using only Occam's razor? This may seem a silly and fun question, but what is the most complex proof that ...
1
vote
2answers
110 views

Why does this Conditional Proof write: T → (T ˅ T) → T?

Source: p 446, A Concise Introduction to Logic (12 Ed, 2014) by Patrick Hurley Here is another example of an argument having a tautology as its conclusion. In this case, since the conclusion is ...
1
vote
1answer
44 views

How does a Statement Function 'make no definite assertion about anything'?

Source: p 456 (chart), 457 (Quote), A Concise Introduction to Logic (12 Ed, 2014) by Patrick Hurley In these examples, the expressions [...] [that I coloured in green], and so on are called ...
0
votes
2answers
186 views

All philosophers are nerds. So, no squares are circles [duplicate]

Can the above argument be valid? If it can, I want to know why, as far as I see, even though the conclusion (no squares are circles.) is true, it doesn't seem to be following the premises (not a ...
0
votes
1answer
115 views

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 ...
0
votes
1answer
381 views

For Universal Instantiation of a Variable, besides notation, does (x)ℱx differ from ℱy?

Source: A Concise Introduction to Logic (12 Ed, 2014) by Patrick Hurley [p 464:] Since, however, the first eight of these rules [of Inference] [hereafter ROI] are applicable only to whole lines ...
0
votes
1answer
284 views

Is falsificationism a reliable scientific methodology?

Initially it seemed to me that falsificationism is a reliable scientific methodology for disregarding hypotheses/theories. Upon some thinking, however, I conclude that it is not. Below I explain why. ...
0
votes
4answers
451 views

How to dissect or parse an 'if' nested within another 'if'?

Source: p 153, Letters to a Law Student, 1 ed (2006), by McBride Section 2 of the Theft Act 1968 (title: “ ‘Dishonestly’ ”) provides that: (1) A person’s appropriation of property ...
0
votes
0answers
85 views

Before (dis)proof, how can you determine the conclusion of given collection of long complicated premises?

Source: p 287, Sweet Reason: A Field Guide to Modern Logic (2010 2 ed) by Henle, Garfield, Tymoczko. [1.] Predicate is the reason we started on deductions. In Sentential, remember, we can verify ...
0
votes
4answers
307 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 least ...
0
votes
2answers
1k views

Conditional statements truth table [duplicate]

Possible Duplicate: How can we reason about “if P then Q” or “P only if Q” statements in propositional logic? I have read in quite a few books that the proposition 'p->q' can be read as either '...
0
votes
4answers
2k views

What exactly does 'Some' mean in Logic?

If the argument (1) Some dogs are carnivores. (2) Some dogs are mortal. (c) Some dogs that are carnivores are mortal. is given, do those 'some dogs' refer to two different groups (dogs might or ...
0
votes
2answers
267 views

How to use “some” and “not all” in logic?

As asked here about the difference between "some" and "not all". I'm looking for a practical example in real world where these two can be applied. Do we have a situation where we can use either of ...
0
votes
3answers
341 views

A Critcism of the Ontological Argument for God

Allow me to present the argument: (1) By definition God is that being which possesses every perfection. (2) Existence is a perfection. (3) Therefore, God exists. Whether you agree is not important,...
0
votes
2answers
137 views

Besides notation, how does (x)ℱx differ from ℱx?

Abbreviate Bound Variable to BV, Free Variable to FV, Universal Generalisation to UG, and Universal Quantifier to UQ. Source: A Concise Introduction to Logic (12 Ed, 2014) by Patrick Hurley [p 456:...
0
votes
1answer
591 views

Is a loaded question a fallacy?

http://en.wikipedia.org/wiki/Loaded_question says that a loaded question = a complex question fallacy. Yet how's it a fallacy? Isn't it a logically consistent, valid (yet militant and treacherous) ...
0
votes
1answer
77 views

A question about taxonomy terms' usage [closed]

I am working on a paper in English and have stuck at taxonomy terms' usage. It is accepted that 'scientific disciplines divide the particulars they study into kinds'. But there are also taxonomy ...
0
votes
3answers
149 views

I search an example of an ad hominem argument, which is not simultaneously an argument from analogy

Incidentally I found an old copy from a book, with this claim: “Hence most ad hominem criticisms are really forms of the argument from analogy” (Douglas Walton, Ad Hominem Arguments, Tuscaloosa, The ...
0
votes
2answers
60 views

Another logic proof problem I'm stuck on :(

sigh stuck on another problem Premises P Conclusion (( ~(Q → R) → ~P) → (~R → ~Q)) I am allowed to use Modus Ponens, Modus Tollens, Hypothetical Syllogism, Simplification, Conjunctions, Addition, ...
-3
votes
3answers
834 views

At which point is an insult no longer ad hominem?

During an argument with some people, I come to the conclusion that they are either stupid, ignorant or liars. Let's imagine that we have 2 guys discussing what color they should be painting a room. ...
-3
votes
1answer
81 views

Fitch Arrow Proofs [closed]

Using the FITCH program and the FITCH derivation rules you should make a proof or derivation of C10 from P5 through P11. P5: ∀x∀y(StrongPref(x,y)→ ¬StrongPref(y,x)) P6: ∀x∀y∀z((StrongPref(x,y)∧...