Modal Logic Semantics | Attic Philosophy

[@linhgia8242]

Thank you for making this video! I love the enthusiasm in your voice, making learning so fun.

[@AtticPhilosophy]

Thanks! Much appreciated!

[@אהלןסהלן]

@@AtticPhilosophy Hey Attic philosophy! Very much like your work and videos explaining this not so taught subject :) Id be happy to give my 2 cebts with some constructive critisicm ^^ Your presentation is very clear, and well communicated, and the visuals are spot on. Theres a bit of a feeling of hopping from subject to subject, from trees to axioms to proofs back to trees again semantics though there were semantics before but again... a bit jumbled up, maybe a bit more of a transition from a topic to another or a table of contents. The explination of each subject feels messy with to few examples, leaves quite a bit to be desired, and to be frank - I don't know if I could say I actually learned how to properly reiterate the skills you introduce, even in the most simplest of way, it seems lacking. Apologies if it seems harsh a bit, thats my feedback and hope it helps!😁

[@Bunnokazooie]

Loving this series so far Dr. Jago. What I would like to see are some examples of good English language deductive arguments that are best proved with modal logic. A good classical logic example of what I mean is something like "It is raining or the dog is not wet ; The dog is wet. Therefore it is raining." Like, I can convert it into symbols in order to prove the conclusion from the premises. It would be nice to see an analogous example for sentences like "It is necessary that X" or even "I believe X" or "I know that X". It would also be nice to see some English-language scenarios which help motivate why you might choose K4 versus K45 versus KB as a "good" foundation for the deductive argument. Or maybe why the extra rules that something like K5 gives you would NOT be appropriate, Hopefully that makes sense. Greetings from the USA!

[@AtticPhilosophy]

Good idea! Here's a simple alethic example: P1 It's necessary that either p or q P2 Not p C Therefore, q Some good examples come from epistemic modalities: 'If one knows that p, then p' as Kp -> p And temporal modalities: 'If it's always going to be p or q, and today isn't p, then today is q' As to why we might prefer one system to another, it depends on how we read [] and . If alethic ('necessary' and 'possible'), then S5 is very plausible: what's necessary is necessarily necessary; what's possible is necessarily possible. But 5 is not so plausible for epistemic uses: we don't know all the things we don't know (~Kp doesn't seem to imply K~Kp).

[@Bunnokazooie]

@@AtticPhilosophy What does epistemic Kp correspond to in alethic modal logic? Box p or Diamond p?

[@AtticPhilosophy]

[]p. It's saying: in all epistemic possibilities (for the agent in question), p.

[@Nicoder6884]

@@AtticPhilosophy The alethic example only works if we assume that every world has an arrow that connects back to itself. Otherwise there could be some world W such that "p v q" is true in every world that W can see, but false in W itself.

[@AtticPhilosophy]

@@Nicoder6884 That's right. Nearly everyone believes that 'necessarily' is factive, which amounts to reflexivity (every world has an arrow to itself). But as you say, it's perfectly ok to have logical systems which lack this feature.

[@robfielding8566]

oh! state machines! that is why i am here, trying to learn TLA+. Box and Diamond are new. state machines easily follow from BNF grammars and sets of variables (ie: TLA), differential equations, and work well with logic.

[@Nicoder6884]

13:28 Distribution doesn't seem to always hold for epistemic modality. It seems like one could know "A --> B" and know "A", but not know "B" since they do not know how to use implication elimination. I also suppose that by that line of reasoning, necessitation does not hold for epistemic modality either; just because a statement is valid does not mean it is known.

[@AtticPhilosophy]

Epistemic modalities are really tricky! The issue is known as 'the problem of logical omniscience': just because something is valid, or necessarily true, doesn't mean we automatically know it. And relatedly, you can know p->q and know p without knowing q. (Although some people deny this!) If you want to do epistemic modalities without these features, you need to go beyond possible world semantics. Either impossible worlds (my favourite), or use some other approach entirely.

[@jacobcastle5925]

Keep up good work!

[@AtticPhilosophy]

Thanks, I’ll try!

[@ravenecho2410]

if it is always the case a -> b, then for any world a -> b [ ] (a -> b) = [ ] a -> [ ] b super clear examples

[@AtticPhilosophy]

Thanks!

[@kantamana1]

I was trying to figure out which modal logic system corresponds to a partial order relation, but it seems that the property of antisymmetri is not included in any of the systems. Or can it be implied from the other properties?

[@EmC-p2y]

I would truly appreciate if you could answer this. I have looked everywhere online, and I believe there is something that is vague about modal logic. Does the valuation function need to have an infinite domain? For example, the valuation function V is defined as V: F x W -> {true, false} , where F is a collection of sentences and W is the set of worlds in the model. It is never specified what kind of set F is. Is it always the infinite set containing all the possible sentences that can be built in the formal language of modal logic (let's call it L)? Or is F just a subset of L? I'm confused about this and I can't find an answer anywhere. Thank you for reading my message

[@AtticPhilosophy]

Valuations assign true or false to each sentence letter, p,q,r etc., not to every sentence of the language. Complex sentences get assigned a truth-value by the recursive clauses, based on a valuation. There are (usually) countably many sentence letters p,q,r… (and so countably many sentences is total). Countable = same size infinity as the natural numbers.

[@EmC-p2y]

@@AtticPhilosophy Thanks, so does V assign a truth value to every single primitive sentence in the whole language L (and never just a finite subset of Lp)? (Lp is the subset of L containing all and just the primitive sentences of L)

[@AtticPhilosophy]

@@EmC-p2y Yes, otherwise, for some p, pv~p wouldn't be true.

[@KCComics]

I can't comprehend w Weather your saying modal or model?

[@PlanetHopf]

These are amazing

[@AtticPhilosophy]

Thanks!

[@tomholroyd7519]

do paraconsistent logic

[@AtticPhilosophy]

Already ahead of you! Try these ones: Paraconsistent logic kzbin.info/www/bejne/opDVmpZ8fsutg9E Three-valued logic: kzbin.info/www/bejne/mKbagIGcir-Ajqc No fact of the matter: kzbin.info/www/bejne/nIuvmGSoZt-Upsk

[@JohnnyTwoFingers]

This binary true or false model makes me nervous, the actual real world ain't like that.

[@AtticPhilosophy]

Sure, language is often vague, but logical sentences are meant to be perfectly precise.

[@SeanAnthony-j7f]

Philosophy is counter intuitive- if you wanted to be a philosopher you need to train yourself for all the people who will oversimplify just because they have preconceived notions about it.

[@JohnnyTwoFingers]

​@@AtticPhilosophyI'm gonna have to rewatch to see wtf I meant by my comment, on a video about modal logic 😂😂🥰