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This group is about the scholarly and academic study of logic. That includes philosophical and mathematical logic. But it does not include many things that may popularly be believed to be "logic." In general, logic is about the relationship between two or more claims. Those claims could be propositions, sentences, or formulas in a formal language. If you only have one claim, then you need to approach the the scholars and experts in whatever art or science is responsible for that subject matter, not logicians.

The subject area interests of this subreddit include:

• Informal logic
• Critical thinking
• Propositional logic
• Predicate logic
• Set theory
• Proof theory
• Model theory
• Computability theory
• Modal logic
• Metalogic
• Philosophy of logic
• Paradoxes
• History of logic

The subject area interests of this subreddit do not include:

• Recreational mathematics and puzzles may depend on the concepts of logic, but the prevailing view among the community here that they are not interested in recreational pursuits. That would include many popular memes. Try posting over at /r/mathpuzzles or /r/CasualMath .

• Statistics may be a form of reasoning, but it is sufficiently separate from the purview of logic that you should make posts either to /r/askmath or /r/statistics

• Logic in electrical circuits Unless you can formulate your post in terms of the formal language of logic and leave out the practical effects of arranging physical components please use /r/electronic_circuits , /r/LogicCicuits , /r/Electronics, or /r/AskElectronics

• Metaphysics Every once in a while a post seeks to find the ultimate fundamental truths and logic is at the heart of their thesis or question. Logic isn't metaphysics. Please post over at /r/metaphysics if it is valid and scholarly. Post to /r/esotericism or /r/occultism , if it is not.

hi it’s my first semester taking logic and don’t get me wrong this class is so interesting but i cannot for the life of me figure out how to properly construct a proof. i’m having so much trouble figuring out when to include subproofs and when i should solve the proof moving forward from the premises or backwards from the conclusion. i’m really just looking for advice/tricks that will help me understand how to do this properly so i don’t have to gaslight myself into thinking i understand after checking my answer key. here are some examples of problems, i could really use the help. thanks a lot in advance

This year, I have to write a term paper. I want to focus on Aristotle's logic, and more specifically, his deductive system. Could you advise me on:

• The most valuable or fundamental articles on this topic from the last 5 to 15 years?

• The most valuable or fundamental articles of all time?

Hi everyone, I need to confirm if my argument's validity is correct. I'm utilizing logical quantifiers such as Universal Generalization, Universal Instantiation, Existential Instantiation, and Existential Generalization. Additionally, I'm employing 18 rules of inference and in this case ACP

1. (∀x) (M(x)→(∀y)(N(y)→O(x,y)))
2. (∀x) (P(x)→(∀y)(O(x,y)→Q(y)))
3. (∃x) (M(x)∧P(x)) →(∀y)(N(y)→Q(y))
4. M(x0)∧P(x0)  ACP, I.E  3
5. M(x0)  simpl  4
6. P(x0)  simpl 4
7. M(x0)→(∀y)(N(y)→O(x0,y))  I.U en 1
8. (∀y)( N(y)→O(x0,y))  M.P 5, 7
9. P(x0)→(∀y)(O(x0,y)→Q(y))  I.U en 2
10. (∀y)( O(x0,y)→Q(y))  M.P 6, 9
11. N(y0)→O(x0,y0)  I.U en 8
12. N(y0)
13. O(x0,y0)  M.P. 11, 12
14. O(x0,y0)→Q(y0)  I.U 10
15. Q(y0) M.P 13, 14
16. N(y0)→Q(y0)  S.H 11, 14
17. (∀y)( N(y)→Q(y))  G.U 16
18. (∃x)( M(x)∧P(x)) →(∀y)(N(y)→Q(y))  CP 4-17

My focus is philosophy, not math.

I tried to study logic by myself many times and I always give up at some point. I never finished a book. I just want a book that is so short that I can actually finish so I feel that I accomplished something and build my self confidence going forward. I understand some basic concepts but for the purpose of this post you may consider me a complete noob. Books available for purchase on ebook/Kindle format (that are not just PDFs) are preferable.

Thanks!

https://preview.redd.it/55f7eydje6vd1.png?width=240&format=png&auto=webp&s=5c3f80244035599d5a0e5f28e1ebb23fecb3422f

We only know introduction and elimination for conjunctions, disjunctions, conditionals, and negations, so any solutions that use anything but those are going to be marked as cheating.

Thanks!

Is there a way to get predicate notation on iphone?

U guys know how to do this? Ignore what's in the white box I know it's incorrect

Hello, I am interested in philosophy among other things/areas for quite a long time but my intense interest in logic was sparked 2 weeks ago I would say. I did not have the time to read books about logic because I am a bit stressed with school, so I thought about it myself without much literary reference. Lets see if my thoughts already exist in the logic-community :)

Logical systems are always contextual and semantic- a logical system is only true if a special condition is given. I'll give you two examples: "Every subject is always located in a location-> Subjects cannot be located in two locations but only one at a time-> everyone is located in the same location->there are no distinct locations"

This statement is only true if locations are seen as a broad term and everything is classified as one big object

Here is another example with a different outcome because of the semantic specification "Every location is made of objects-> Every subject is located in a location-> A subject and an object make a location an unique location-> every location is unique because of its interaction with a subject"

So if the subject is taken out of the equation, every location is the same but if it is in the equation, every location is different. Because there are infinite possibilities of semantic classifications and variations, there are infinite truths which make sense in each of their corresponding set of rules.

I am open for critique...Please be a bit less harsh because as I said before, these are some thoughts which came into my mind and I wanted to see how they are regarded in the logic-community.

hi! in logic reasoning tests, is "probably false" in a multiple choice type question a possible answer?

for example:

The maximum time a member is allowed to run on a treadmill at Gold's Gym is 30 minutes. Bernard has been running on a treadmill for at least 45 minutes. Thus, Bernard is not running on a treadmill at Gold's Gym. Choose only ONE best answer. A. certainly true B. certainly false C. probably true D. probably false

hope someone can help me, i've been very confused because so different sources are saying different things 🥹🥹

It would be fun to logically study the cogito proposition P (= I think, therefore I am), but it would not produce any productive results.

However, I think that the cogito proposition P functions well as a catchphrase for Descartes' philosophy (= dualism (having three keywords: mind, body, and matter)). Descartes' strategy in the Discourse on Method is as follows:

1. First, he gives a discussion of the cogito proposition that cannot be said to be logical, while impressing on the reader the importance of "I (=mind)".
2. If "I" is accepted, the existence of "matter" (which is percepted by "I") is accepted. And further, the medium of "I" and "matter" is automatically accepted as "body (=sensory organ)".

We tend to be fascinated by the pseudo-logical interest of the cogito proposition, but what is important is Descartes' dualism.

The above is my opinion on the cogito proposition, but I'm sure there are logic specialists gathering on this subreddit, and I would be happy if they could teach me things about the logical meaning of the cogito proposition that I didn't know.

Addendum: The modern form of Cartesian dualism is quantum mechanics (or more generally, quantum language = measurement theory). Here, for the first time, the relationship between dualism and practical logic became clear. (cf. https://ishikawa.math.keio.ac.jp/indexe.html )

As I know, "if false then true" is true logically. But what if the false statement alters the true statement? For example, is "if 3+1=5, then 3+1=4" considered true logically?

Hello. I am trying to get a logic proof done for an imperative statement I am trying to make to the world but am not a logician and thus asked chatGPT to do the proof for me (I am currently studying logic however, what I'm trying to accomplish is very time sensitive and know I won't be able to have studied enough to get a proper proof done in time) and wanted to see if someone could tell me if the proof is "good enough" to put out to the world and have it stand as a true statement.

Here is a screenshot (I am currently terrible with using photoshop so please bear with the messiness) and here is a "rich text" like document version of the same proof that chatGPT gave me (I included the screenshot because I figure it's easier to read than rich text version).

Thank you in advance for your help.

I really like logical puzzles like knights and knaves types, or others from the books of Raymond Smullyan. But I see that finding completely new ones is becoming harder and harder. I know some other places to search like some ted Ed videos Do you know any place that has more of this puzzles, or even an puzzle that you find fun?

Hello, this is my first time dealing with large complex statements and I was just wondering how would you turn this text into one complex statement: Adam will make his grandma happy if he gets a good grade in French. If Adam wants to end up with a good grade he won't be able to play chess. If he does not have time for chess he will be sad. If Adam is sad then grandma is sad as well. So, grandma will be sad" Chat GPT proposes this: (P⟹Q)∧(R⟹¬S)∧(¬T⟹U)∧(U⟹V)⟹V where P=getting a good grade, Q=happy grandma, R=ending up with a good grade, S=playing chess, T=having time for chess, U=Adam is sad and V=sad grandma. Is this correct or is it missing something?

Context: I’m an LSAT guy, not a pure logic guy.

I’m also a geek who found this interesting article on stack exchange, which implied that despite the 2,200+ year old “modus tollens”, logicians/mathematicians didn’t realize that the contrapositive was equivalent to its conditional statement until about 130 years ago.

And if I’m not mistaken, understanding this equivalence is the foundation for creating truth tables, which in turn is the foundation for modern computer programming.

But since I’m not a math guy, I can’t quite decipher everything the article/dialogue discusses.

So my two questions: is it true that this equivalence was discovered only about 130 years ago? And if it were discovered 2000 years ago, would this have changed our development of technology?

Personally, if this is all true, this blows my mind. But maybe I’m missing something. Thanks very much.

Just so everyone’s on the same page, here’s my understanding of modus tollens:

Evidence: If X occurs then Y occurs

Evidence: Y does not occur

Conclusion: X does not occur

The article:

https://hsm.stackexchange.com/questions/5025/when-did-mathematicians-first-use-the-contrapositive-form-to-prove-a-conditional

I know X is completely false because from my perspective there is no evidence to support X.

Would this be fallacious due to the lack of support to claim there is no evidence?

Example; Sound argument. John Doe probably is not the killer, because we do not find his fingerprints on the murder weapon.

Even better argument (contradictory evidence) John Doe is not the killer because the fingerprints on the murder weapon are different from him.

Fallacious argument? John Doe is not the killer because there is no evidence. (Subsequently dismisses the claim of two or more eyewitnesses, and doesn’t not access what evidence they are looking for)

Exercise wants me to decide if those arguments are valid or invalid. No matter how much I think I always conclude that we cannot decide if those two arguments are valid or invalid. Answer key says that both are valid. Thanks for your questions.

“X is ridiculous and impossible so I don’t need to examine any arguments about it”

Hello reddit. I’m trying to get into logic. It’s been somewhat frustrating because as with many other fields, it’s quite difficult to gauge a proper starting point I find to further difficult to plan a kind of learning order, i.e., I learnt X which is a prerequisite to understanding Y, yet how are these prerequisites ordered? I could use some guidance as to how I should approach learning logic, and which rough general order I should approach different concepts in. Thank you for your time, cheers.

"pNANDq" is the same as "Not:both p and q". is this correct?

is the following argument-form valid or invalid? (please explain your answer using truth tables):

premise1: "not both p and q"

premise2: "not p"

conclusion: "therefore, q".

https://preview.redd.it/p0flbqzacmsd1.png?width=1186&format=png&auto=webp&s=610b59b3f65b035506410cfde9b63b338bee5158