Existence and Logic | Attic Philosophy
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- เผยแพร่เมื่อ 9 ก.ค. 2024
- Existence is a tricky concept, especially in quantified modal logic, where we have different possible worlds with different possible things in them. In this video, we take a look at some of the philosophical and logical issues surrounding existence and possible entities in logic.
00:00 - Intro
00:33 - The problem of existence
01:16 - Identity & Existence in QML
02:32 - Why the problem arises
03:55 - De Re vs De Dicto versions
04:42 - Proof theory version
06:36 - Variable Domain Semantics
07:04 - Change what ‘Ex’ means
08:03 - Analogy: existence and the past
08:51 - Thick vs thin existence
09:49 - Possible existence
10:59 - Summing up
More videos on modal logic coming next! If there’s a topic you’d like to see covered, leave me a comment below.
Links:
My academic philosophy page: markjago.net
My book What Truth Is: bit.ly/JagoTruth
Most of my publications are available freely here: philpapers.org/s/Mark%20Jago
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#logic #philosophy #possibility
Thanks for making these videos! They're are easier to understand than every other resource on modal logic I've found. There is one thing I don't get about the semantics of quantifier operators though. The way I understand the existential operator is as referring to existence in a platonic sense, like when we one says "for every prime there exists a larger prime". It seems to me like a weird choice of semantics to understand existence as physical existence. It also seems to make the system less expressive, because there is no way to express existence in every possible world, while the converse is true: if existence means existence in every possible world, I can always define a function F(w, x) as true if x physically exists in world w, and then instead of saying "∀x P, w" I can say "∀x F(w, x) → P, w". This would also make the paradox you mention not a paradox anymore since whenever something exists, it would exist in every possible world, which is what one would expect of abstract entities like numbers. So why is it that the existential quantifier is understood as ranging over the set of things that exist in the one possible world only, and are there any alternative interpretations I could look into? Thanks!
Amazing video! I've never seen this problem explained so simply and elegantly. A great resource!
Thanks! I've taught it for several years, I guess that helps getting it clear
The thin concept of existence may handle the 'non-actual' well, but how does it account for the genuinely substantive - i.e. the notion of 'things' from which everything is composed? Granted, in modern physics, there is a case for only relations and not actual bits of stuff . But how, under the 'thin' account, do we capture, logically, the notion of absolute things? I guess we just kind of posit them? Maybe as a general case or a theory or special modifier? - anyway, this is all fascinating stuff!
Well, real physical objects would exist in the full, *thick* sense, whereas only those difficult entities - the merely possible, maybe the fictional entities, maybe the abstract ones - would exist only in the *thin* sense.
@@AtticPhilosophy Thanks! So, two categories of existence, maybe more? Philosophical richness, indeed.
Hi! Loving the videos, thanks so much for making them :)
Was curious whether you'll do one on two-dimensional semantics and issues surrounding it?
Great suggestion! Thats quite an advanced topic & I've never worked out what's the simplest way to present it, but I'll give it a go
Any chance you’d consider making a video about Free Logic? May be a useful complement to this and related videos?
Great idea! That's definitely something I should cover soon.
Thin existence: conceptual
Thick existence: realized
Please help, I know nothing.
Thank you, Dr Jago! Is this view related to the view you developed in your impossible worlds book?
You're welcome! The views aren't really related. Those who talk about 'thin existence' usually reserve it for possible entities, since most people don't want to say anything impossible exists in any sense.
Thank you so much for making this kind of videos. I find the idea of thick and thin existence really interesting. Are there any books, articles or works of particular philosophers that I can read further if I want to dig deeper on this idea? Thanks a lot!
Graham Priest’s book, Towards Non-Being, is really interesting on this topic.
@@AtticPhilosophy Thank you so much for the suggestion.
The ironic thing about this is that the whole system of symbolic logic and it's ideas don't really even exist in the sense that the material world does. If Pegasus can't be understood to exist at least in some symbolic sense, then why should any character of the language of logic?
Hi Attic,
I've already mastered basic logic and reason (truth tables, fallacies) and I've taken a class in symbolic logic as well, and I feel comfortable with that too. What are the next steps (topics) in learning logic?
Hi Vinny, there's loads of different directions you could take. If you want to learn more *kinds* of logic, there's modal logic (see the videos here), intuitionistic logic, and many-valued logic (videos on these coming soon). Or you could go deeper into the logic you've already looked at: proof theory (natural deduction, proof trees, sequent calculus), or meta-logic (soundness, completeness, decidability). Or you could look at philosophical issues (should Excluded Middle or Non-Contradiction be accepted?) Videos on that coming here soon.
@@AtticPhilosophy Thanks Attic!
@@AtticPhilosophy any plans to cover predicate logic?
How do you model haptia as a nexus of perspectives, a model of models? I'm not saying she didn't physically exist, but that the way her meaning exists as a summed up being (rather than as separate atoms or whatever) is all mitigated through perception. What role does that play in structural logic?
Is this the work of a random word generator?
@@AtticPhilosophy No. And that's a pretty harsh thing to write.. Are you interested in what I'm trying to ask, or just trying to be a jerk? The question is asked in good faith.
@@AtticPhilosophy And also, even if the wording isn't great, the idea isn't that hard to grok.
@@dylanl2258 The words in the question seem completely random. I don't know what haptia is, or 'nexus of perspectives', or what any of that has to do with a video on Quantified Modal Logic. Are you asking how logic represents a person or an idea or something like that?
Can you please clarify what you are talking about?