Re: [ontolog-forum] A Question About Logic

[Thomas Johnston <tmj44p@xxxxxxx>]

Reply to Leo's Oct 12^th comment.

Leo:

It's easy to get sidetracked, and I think truthmaker theory, fictional objects and negated things can be put aside for the purposes of the position I've taken which is, to be as clear as possible, this: changing from a statement to its negation shouldn't entail a change from or to an ontological commitment to what the statement is about (i.e. what its subject term represents). Yet standard predicate logic, and the deMorgan's equivalences, do just that. I have to either adjust my intuitions, or take a position I am unqualified to follow through on – namely that something's wrong with predicate logic and something else should be put in its place. A few comments on from yours, Pat Hayes suggests my intuitions need adjustment. When I get to Pat's comment, I will make a few suggestions about adjusting predicate logic – as ridiculous as it is for a non-logician to do so. As on previous occasions when I've taken a prima facie ridiculous position, I think of Martin Luther:

Heir ich stehen.

Ich kann nicht anders.

BTW, I take your "If ontologies are not necessarily real" to be referring to possible worlds, not just as novels and other forms of stories, but as the kinds of things we can use in doing proofs in modal logic. That's right, isn't it? For that issue, too, I think we can finesse it in my quest to find out what's wrong with my ontological / predicate logical intuitions.

On Monday, October 12, 2015 7:03 PM, "Obrst, Leo J." <lobrst@xxxxxxxxx> wrote:

One problem is that some folks view an ontology as just a logical theory (and how that is defined, e.g., do you worry about the “truth of a theory”?), in which case, the bound variables don’t have to correspond to anything that is real (depending on your notion of “truth of a theory”), hence there is no ontological commitment (on this Quinean view of ontological commitment) if ontology is taken to be of the real world.

 

Example: one can have a logical theory about Hobbits, and though the theory commits you to Hobbits, there is no requirement that Hobbits exist in the real world. The theory is “true” with respect to the Hobbit world. Squinting a bit, perhaps it commits you to an irreal fictitional ontology of Hobbits in that fictional world. It really depends on what you mean by “the truth of a theory”.

 

By the way, I don’t think that not using a conditional (e.g., in your examples of existential bindings, these are conjunctive and not conditional bindings) means anything, as far as the ontological commitment per bound variable view intends. However, if the binding of an X in a predicate P in P(X) (where P might be something like “is a natural number”), seems to commit one ontologically to natural numbers, I think instead that it commits you only to the particular theory’s commitments, and so remains just logical, not ontological.

 

If ontologies are not necessarily real, then all bets are off, I think. If they are real, then many would say that to establish ontological commitment requires a “truth-maker” for the thing you are ontologically committing to. At least, that’s my understanding, incomplete as it might be. Personally, I think that logical variable binding is a necessary, but not sufficient notion for ontological commitment. I’ll allow the hogwash-callers to intercede here.

 

Finally, concerning negation, most ontologists of the realist persuasion will argue that there are no negated/negative ontological things.

 

Thanks,

Leo

 

From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx [mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] On Behalf Of Thomas Johnston
Sent: Monday, October 12, 2015 5:01 PM
To: [ontolog-forum] <ontolog-forum@xxxxxxxxxxxxxxxx>
Subject: [ontolog-forum] A Question About Logic

 

Oct 10, 2015. A Question About Logic.

 

I have a question about logic, which I hope the logicians in this group can help me with.

 

In predicate logic, universal quantification does not involve ontological commitment, whereas existential quantification (as the name suggests) does. To illustrate:

 

"All dogs are renates" is formalized as "If anything is a dog, it is a renate".

In notation: Ux(Dx --> Rx)

 

"Some dogs are friendly" doesn't require translation, and in notation is: Ex(Dx & Fx).

 

(I use "U" for the universal quantifier, "E" for the existential quantifier, "-->" for material implication, "~" for not, "&" for conjunction, and "<--->" for the metalogical operator of being equivalent to.)

 

So Ex(Dx & Fx) says: "There exists a dog such that it is friendly." "There exists"; in other words, an ontological commitment to the existence of at least one dog.

 

But Ux(Dx --> Rx) says: "If anything is a dog, it is a renate". No ontological commitment here.

 

This is all very familiar, of course. But here's a question: why, in the formalization of predicate logic, was it decided that "Some X" would carry ontological commitment whereas "All X" would not? (I think the question has been asked and answered before, but I don't recall what the answer is.)

 

Now let's move on to the deMorgan's equivalences, in which the negation of a universal quantification is an existential one, and vice versa. In notation:

 

~Ux(Dx --> Rx) <---> Ex(Dx & ~Rx)

~Ex(Dx & Fx) <---> Ux(Dx --> ~Fx)

 

In English: "It is not the case that if something is a dog, then it is a renate" is equivalent to "There exists something that is a dog and is not a renate". And: "It is not the case that there exists a dog which is friendly" is equivalent to "If something is a dog, then it is not friendly".

 

I've worked with deMorgan equivalences for so long that they seem intuitively right to me. But now notice something: negation creates and removes ontological commitment. And this seems really strange. Why should negation do this? My being ontologically committed to something doesn't have anything to do with negation; it's simply the _expression_ of my belief that the world contains something, of such-and-such a type.

 

Note, too, that Aristotle's square of opposition didn't have this strange feature. The negation of "All dogs are renates" is simply "Some dog is not a renate", and the negation of "Some dogs are friendly" is simply "No dogs are friendly".

 

I suspect that this strange feature, of negation having ontological import, has something to do with Frege's meta-logical interpretation of properties (predicates) as sets, i.e. as purely extensional objects. But I don't know, and that's what I asking about.

 

I'd also like to know if there are formal logics which do not impute this extravagant power of ontological commitment / de-commitment to the negation operator in predicate logics.

 

As recent earlier comments have indicated, I'm currently on the track of semantics, primarily of the cognitive variety, and definitely including the diachronic variety. And so this question is well-off that track. It came up as I was (re-)reading a book which, although it is 25 years old, I highly recommend:

 

Meaning and Grammar: an Introduction to Semantics (MIT, 1990), by Gennaro Chierchia and Sally McConnell-Ginet

 

What dates this book is that it is heavily influenced by Chomsky who, at the time of the book's publication, had left behind (i) transformational-generative grammar, (ii) extended transformational-generative grammar (the result of the "linguistics wars"), and was in either his (iii) principles and parameters incarnation, or (iv) his X-bar theory incarnation, or somewhere between the two.

 

But the book is at least as deeply indebted to "west coast" semantics, i.e. the Montague program, and, as it seems to me, the Chomskyean associations do not run deep enough to tie this work to any of Chomsky's later repudiated positions.

 

Thanks,

 

Tom

 

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