Questions tagged [logic]
For questions about logic, whether it concerns syllogistic logic, mathematical logic or the nature of logic itself.
2,872
questions
6
votes
7answers
2k views
If you used intuitionistic logic in real life, would you not sound absurd?
Intuitionistic logic does not include the law of the excluded middle and double-negation elimination.
I imagine a real-life conversation with an intuitionist might go like this:
Amy said you didn't ...
-4
votes
1answer
22 views
Is there a person in the world that is smarter than me? [closed]
So, is there?
The catch is that I would not accept if a person has greater expertise in-- something. Simply knowing more about quantum mechanics, fishing and politics doesn't count as smarter.
0
votes
1answer
23 views
Instantiation and Generalisation and Formal Logic
I was wondering what generalisation and instantiation were exactly because my notes claim it to be:
Generalisation: "from elementary to complex propositions"
Instantiation: "from ...
0
votes
0answers
53 views
Is there a semantic version of the deductive theorem for an arbitrary logic system?
As far as I know, any logic system always defines its own semantics $\models$, but doesn't necessarily have a proof system or $\vdash$ which is complete and sound with respect to $\models$.
In an ...
14
votes
2answers
2k views
Why did the mid-19th century and earlier thinkers fixate on one-place predicates?
A book I'm reading mentions the following:
A major barrier to the development of first-order logic had been the
concentration on one-place predicates to the exclusion of many-place
relational ...
-2
votes
0answers
32 views
What if purpose has come by the occurrence? [closed]
A question (especially from those who believe, "I exist. Therefore there has to be a purpose")
I was wondering what if we are living in a multiverse, with many parallel timelines.
Then this ...
1
vote
1answer
38 views
Relationship between Principle of sufficient reason and Law of identity [closed]
I have an intuition that one can derive the principle of sufficient reason from the law of identity or non-contradiction but i don't know how.
If someone knows I'd like some help.
3
votes
3answers
282 views
Is it possible to define Truth?
I hope this is the right place to ask a question like this. I'm a student, I haven't studied philosophy and I'm not familiar with all of the famous philosophers, so this question probably already have ...
3
votes
1answer
46 views
How does Consequentialism handle uncertainty?
E.g.
Suppose you are a Consequentialist faced with a variation of the trolley car problem. Your options are to save five people with a 20% likelihood or one person with a 100% likelihood. Which option,...
-3
votes
0answers
50 views
How does our death affect our perspective on the law of non-contradiction? [closed]
..I'm sorry if my question seems a little rough, but this has been something that has been bothering me and I don't know where to research this.
Does the law of non-contradiction end when our life ...
0
votes
1answer
54 views
How would you translate āAnything a knave claims is falseā into Predicate Logic?
I am having trouble translating this sentence into Predicate Logic: "Anything a knave claims is false" (or "If x is a knave and x claims y, y is untrue.") I have pasted two ...
-1
votes
0answers
22 views
Identify the logical fallacy
I was hoping someone could identify any logical fallacies in this image. I would also appreciate it if someome could give me tips on how to find out if a logical fallacy is present and how I can find ...
2
votes
4answers
333 views
How can we differentiate between change and progress in the area of history and natural sciences?
I'm studying a branch of philosophy that is considered with knowledge.
I'm studying theory of knowledge(epistemology) and I want to use faith, reason, and memory as tools for carrying this ...
-2
votes
3answers
197 views
How to reconcile the fact that mathematical proofs are logical implications with the lack of a formal calculus equivalent to the logical implication? [closed]
Theorems follow from axioms. That is, theorems are the logical consequence of axioms. Thus, mathematical proofs are essentially deductive. Proofs are all essentially logical implications. There is ...
16
votes
10answers
7k views
What is the name of this fallacy: Is 101 binary or decimal?
A similar example would be of binary and decimal number where we are not sure about the number system or the person who proposed a number is not remotely available to disclose about number system.
e....
4
votes
1answer
145 views
What are the advantages of Aristotle's term logic over predicate logic?
I have read Wikipedia's term logic entry, and the quote by Gareth Evans in the Revival section that's supposed to argue for term logic's advantages over predicate logic:
"I come to semantic ...
-1
votes
0answers
16 views
Deontic Logic (resources) [closed]
Does anyone know good resources to learn or study Deontic logic? It might be books, or other resources.
0
votes
1answer
131 views
How shall I understand Wittgenstein's comment on Russell's work?
Ludwig Wittgenstein said
Russellās books should be bound in two coloursā¦those dealing with mathematical logic in red ā and all students of philosophy should read them; those dealing with ethics and ...
0
votes
1answer
39 views
How to prove that the axiom H is valid in the following frame
To prove incompleteness of KH, I have to prove that the axiom H is valid on the following frame:
Axiom H goes as follows:
ā”(ā”pāp)āā”p
I don't know how to prove this, but here's one idea that's half ...
0
votes
0answers
34 views
Alessio Moretti's graphs
Moretti and his colleagues are at the head of a school of logic focused on the tradition of the Square of Opposition and similar graphs/diagrams. Besides a strong thesis of logical form depending on/...
0
votes
2answers
135 views
A case of vacuous truth : Have you taken part in your department's open discussion session already?
Today I encountered a vacuously true case. But I am not so sure, so please help examine it.
It was from a question form that asks:
Have you taken part in your department's open discussion session ...
0
votes
1answer
64 views
What is this snippet from Frege's Begriffsschrift saying?
I have no background knowledge in logic so I am a little lost about where to begin.
This is the photo I am trying to learn about and it is from Fregeās Begriffsschrift.
0
votes
0answers
62 views
Computing Premises from Consequence
We write 'If A, then B' to mean that if A is true, then B must be true because B is a logical consequence of A i.e. it is impossible for A to be true but B to be false.
Let us consider one such ...
5
votes
5answers
297 views
What separates mathematics from logic? Can “mathematical” operations be applied to logical systems?
In my 'Introduction to Logic' class, my professor told us that half of the class will be based on "mathematical" operations withing logic. After looking through the textbook, I realized that ...
0
votes
3answers
103 views
Can classical logic hold without causality?
Consider a universe where causality failed to hold. Would that universe be described by classical/standard logic? Or would we have to use a radically different logic where causality was not necessary? ...
0
votes
1answer
42 views
Logic question about the sum of one's free choices
If each moral choice a person makes is free (as in free will) it seems to follow that the sum or totality of all those choices is also free. In other words, if each individual sin can be avoided, then ...
2
votes
1answer
55 views
What are some of the struggles that come with teaching formal logic? [closed]
I'm currently an undergraduate student who wants to do research on the pedagogy of formal logic. As a result, I wanted to know what are some challenges that instructors (or even students for that ...
2
votes
1answer
41 views
Where in Aristotle's Topics did he say there's no exact/clear way to distinguish two concepts?
I've heard that Aristotle supposed in his Topics that there's no exact/clear way to distinguish two concepts. What exactly did he say?
1
vote
1answer
138 views
Is it true that if an argument is invalid, any argument of that logical form must be invalid?
I am stuck over whether these statements are true:
First: "If an argument is invalid, any argument of that logical form must be invalid."
Second: "There may be invalid argument with ...
0
votes
0answers
95 views
how to translate the following sentence
Either it is not the case that Gonzolo play music and does not go to concert,or it is not the case that he does not read book and does not play football.
P:Gonzolo play music , Q: Gonzolo go to ...
1
vote
1answer
32 views
if [if (if P then Q) then (if P then R)] then [if P then (if Q then R)]
i am new in logic course, i saw an question in my book. it says that show the following argument is valid by using natural derivation rules.
if [if (if P then Q) then (if P then R)] then [if P then (...
0
votes
1answer
54 views
Why Frege thinks geometry is synthetic?
Frege believes that arithmetic is analytical. Why not Frege thinks geometry can be reduced to arithmetic by coordinate system or something else?
0
votes
0answers
27 views
Why is a material condition true if its antecedent is false? [duplicate]
So I ran into the "drinker's paradox" the other day, which compelled me to learn about the nature of the logical material conditional. But when I studied the truth table (below) I got pretty ...
-1
votes
1answer
39 views
Can you give other examples of skeptical hypotheses that haven't been mentioned yet?
I need some help with my philosophy homework. We were told to formulate our own skeptical hypothesis and use it as part of a radical skeptical argument, and that the skeptical hypothesis needs to be ...
1
vote
0answers
43 views
How should I think about the probability of a causal effect? [closed]
This is a burning question that I've always had. In particular I would love to learn more about uncertainty and non repeatable events. Especially whenever you can't use complicated math and run ...
2
votes
1answer
38 views
When to use logic symbol variants? [closed]
Many logical operators seem to have multiple variants:
Material implication: ā, ā, ā
Negation: Ā¬, ~, !
Conjunction: ā§, Ā·, &
Disjunction: āØ, +, ā„
etc.
Are there differences in their usage (e.g., ...
2
votes
1answer
237 views
What fallacy is this? Ignoring rate of change
What is this fallacy?
"I threw a ball onto the roof. Which way did gravity pull it? Well obviously because the ball started on the ground level and ended up on the roof then gravity must have ...
2
votes
1answer
52 views
What is the literal meaning of “The only thing that I know is that I know nothing”? (Is not knowing anything a knowledge?)
If a person says, "The only thing that I know is that I know nothing." What exactly does that mean (not metaphorically), literally?
If the only thing they know is that they know nothing, ...
2
votes
1answer
63 views
Choice and action
Moore highlighted the connection between asserting and believing by making note of how odd, "It's raining but I don't believe it" (as if to say "I don't believe it's raining but it is&...
2
votes
3answers
91 views
Are There Finitary Logical Constraints on Converting Recursive Syntax to Semantics?
From the logical standpoint can we continue these series on and on and still be able to make sense of it?
1. I know <--- no problem
2. I know ...
14
votes
12answers
11k views
Why is it that the statement “All goblins are yellow” does not contradict the statement “All goblins are pink?”
From what I know, I think it has something to do with vacuous truths, but my understanding is not quite there yet.
0
votes
1answer
42 views
Why is āxāA P(x) equivalent to āx(xāA /\ P(x)), but āxāA P(x) is not equivalent to āx(xāA /\ P(x))?
I know that āxāA P(x) is only equivalent to āx(xāA -> P(x)), but why isn't it equivalent to āx(xāA /\ P(x))? I can use the laws in logic to compare the two, but I want an intuitive reason as to why ...
4
votes
5answers
85 views
Intuitively, why does the disjunction equivalent of the conditional statement “If you study hard, then you'll pass the test” make sense?
This is of the form P -> Q, which is equivalent to ~P \/ Q. The equivalent statement would be the following: "Either you don't study hard, or you'll pass the test." My question is, why ...
11
votes
1answer
1k views
How do you differentiate between At least one X and Exactly one X in predicate logic?
Here are the following two sentences.
At least one person speaks English.
āš„E(x)
Exactly one person speaks English.
Instead of āš„E(x), what do I write?
0
votes
1answer
29 views
How to read modal logic's countermodels?
I'm new to Modal Logic and currently playing a tree proof generator just to see how some stuff work, but I can't read the countermodels that the algorithm gives me when my proposition is invalid. I (...
1
vote
3answers
118 views
can an argument containing a contradiction be valid argument
I know that validity has nothing with truth of the conclusion or with how good argument is in general, and an argument is valid iff the truth of its premises guarantees the truth of its conclusion.
...
0
votes
1answer
28 views
Is my interpretation of “and” correct in these statements?
Let A mean "Equation A has a solution" and B mean "Equation B has no solution." I am a little confused, so I wrote down some possibilities and I wish to see if my interpretation of ...
-1
votes
2answers
40 views
Question about fitch 6.19 proving A or C from premises A or B and -B or C
How to prove A or C from premises A or B and -B or C. Am using fitch and have been stuck on this for an hour
1
vote
1answer
87 views
Does the truth value of a material conditional depend on context?
Suppose the following material conditional "If 1+1=2 then Moon is made of cheese". The antecedent refers to the context of mathematics. In that context "1+1=2" is true. Whereas &...
-1
votes
1answer
57 views
Requesting help with designing curriculum (Logic)
I am currently a math major in university who wants to design my own area of study/major, specifically in Logic. I was wondering if I could get some help on how Logic sets itself apart from philosophy?...
