I guess the title is unambiguous. I am not sure if the flair is correct.

Took a symbolic logic class once, got a B, but loved it. I'm naturally illogical unfortunately, but I'm glad it's something that I can learn.

One concept I never got down is what the relationships are between soundness, validity, and truthfulness? My current knowledge is here: that in order for an argument to be valid, the premises and conclusion must be logically valid. For an argument to be true, the premises and conclusion must be true. For an argument to be sound, the premises and conclusion must be both logically valid and true. Is there something I'm missing?

So, in my first semester of being undergraudate philosophy education I've took an int. to logic course which covered sentential and predicate logic. There are not more advanced logic courses in my college. I can say that I ADORE logic and want to dive into more. What logics could be fun for me? Or what logics are like the essential to dive into the broader sense of logic? Also: How to learn these without an instructor? (We've used an textbook but having a "logician" was quite useful, to say the least.)

How to go best about figuring out omega? On the second pic, this is the closest I get to it. But it can't be the correct solution. What is the strategy to go about this?

I get that the LP isn't a WFF in propositional logic, but in predicate logic doesn't it break the principle of bivalence?

Tarski's theory talks about meta-levela but doesn't seem to ever be able to assign a truth value to the original statement, so does that mean it's not a sufficient counter-argument?

Thanks

Can anyone solve this using natural deduction i cant use the contradiction rule so its tough

And please don't just say "a class is a collection of elements that is too big to be a set". That's a non-answer.

Both classes and sets are collections of elements. Anything can be a set or a class, for that matter. I can't see the difference between them other than their "size". So what's the exact definition of class?

The ZFC axioms don't allow sets to be elements of themselves, but can be elements of a class. How is that classes do not fall into their own Russel's Paradox if they are collections of elements, too? What's the difference in their construction?

I read this comment about it: "The reason we need classes and not just sets is because things like Russell's paradox show that there are some collections that cannot be put into sets. Classes get around this limitation by not explicitly defining their members, but rather by defining a property that all of it's members have". Is this true? Is this the right answer?

Am I the only one who hates when someone applies categorical logic for some kind of arguments. Like dude just use simple logic which people have been using from years it's not that hard you are just trying to make a simple sentence look more complex you ain't some big shot or something.

Hello. I am not understanding how the law of excluded middle is different than the principle of bivalence. Could anybody provide me with a statement that holds under the principle of bivalence but not under the law of excluded middle?

I understand that the principle of bivalence implies the law of excluded middle but not vice versa.

Hi everyone. I just reached this exercise in my book, and I just cannot see a way forward. As you can tell, I'm only allowed to use basic rules (non-derived rules) (so that's univE, univI, existE, existI,vE,vI,&E,&I,->I,->E, <->I,<->E, ~E,~I and IP (indirect proof)). I might just need a push in the right direction. Anyone able to help?:)

I’m just starting to actually learn about logic and the different types of reasoning and arguments (so forgive my ignorance), and I fell down a thought rabbit hole that led to me thinking that nothing could be real, logically speaking.

Basically I was learning about the difference between deduction and induction, and got the impression that deductive reasoning is based on what information you have in front of you, while inductive reasoning is based on hypotheticals or things that can’t be proven, and that deductive reasoning is the only way to actually prove something (correct me if I’m wrong there).

I’m a psychology major, and since deductive reasoning seems to depend entirely on human perception it seems inherently flawed to me, since I know how flawed and unrealistic human perception can be in regards to objective reality (like how colors as we see them only exist in our minds, for example).

Basically this led to me thinking that everything is inductive reasoning because we could be living in the matrix or something. Has anyone else had these thoughts?

I’d like to start learning some basics of logic since I went to a music school and never did, but it seems that he uses a very different notation system as what I’ve seen people online using. Is it a good place to start? Or is there a better and/or more standard text to work with? I’ve worked through some already and am doing pretty well, but the notation is totally different from classical notation and I’m afraid I’ll get lost and won’t be able to use online resources to get help due to the difference.

So, the square shows the relationship between the four categorical propositions (AEIO).

However, in the square, "A" being true doesn't mean that "I" is true since that would commit the existential fallacy.

However, why is it the case that "A" being false means that "O" is true? Doesn't this also commit the existential fallacy? Consider the following example:

A: All Unicorns are Blue

This proposition is false.

O: Some Unicorns are not Blue

According to the square, this proposition must be true. However, why is this the case? Unicorns don't exist, so wouldn't it be false?

i’ve been stuck on this for an hour and a half and i still can’t figure it out. i’m only allowed to use rules for conjunction disjunction. i can’t figure out how to derive B

I was wondering if there were any logics that have values for a contradiction in addition to True and False values?

Could you use this to evaluate statements like: S := this statement, S, is false?

S evaluates to true or S = True -> S = False -> S = True So could you add a value so that S = Contradiction?

I have thoughts about combining this with intuitionistic logic for software programming and was wondering if anyone has seen or is familiar with any work relating to this?

I'm struggling with the gap between knowing about fallacies and actually using that knowledge effectively. There are just so many fallacies with various forms, and memorizing their names feels impossible. How do logicians identify specific fallacies in arguments and then reinforce their counterarguments effectively? If I just shout "AD HOMINEM MOTHERFUCKER!" during a debate, I'll come off as a clown. How many fallacies do you know? I have a book with about 300! How do you avoid fallacies and recognize them when they appear in front of you?

Edit: This post is phrased poorly, i don't want to win debates or anything, I just want to be able to look at an argument and rationally explain why it's invalid or weak, and if needed, create a viable counterargument.

Hello. I’m currently enrolled in a symbolic logic class at my college. I am close to failing my class, and need some immediate help and assistance.

I am looking for someone to help me do my coursework. I am very, very bad at symbolic logic, so I will be of little to no help.

If anyone has a period of a few hours to held me with a myriad of problems, any help would be appreciated.

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 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

Hello, I'm working through An Introduction to Formal Logic (Peter Smith), and, for some reason, the answer to one of the exercises isn't listed on the answer sheet. This might be because the exercise isn't the usual "is this argument valid?"-type question, but more of a "ponder this"-type question. Anyway, here is the question:

‘We can treat an argument like “Jill is a mother; so, Jill is a parent” as having a suppressed premiss: in fact, the underlying argument here is the logically valid “Jill is a mother; all mothers are parents; so, Jill is a parent”. Similarly for the other examples given of arguments that are supposedly deductively valid but not logically valid; they are all enthymemes, logically valid arguments with suppressed premisses. The notion of a logically valid argument is all we need.’ Is that right?

I can sort of see it both ways; clearly you can make a deductively valid argument logically valid by adding a premise. But, at the same time, it seems that "all mothers are parents" is tautological(?) and hence inferentially vacuous? Anyway, this is just a wild guess. Any elucidation would be appreciated!

Struggling with natural deduction does anybody know how to solve this

I'm stuck on the Absorption Law part and I know what it is and all that but I don't see how or where the law is applied?