HDTenEightyP/NetNews huggingface dataset:
From: e343mh@tamuts.tamu.edu (Michael Hand)
Subject: Re: A only if B
Organization: Texas A&M University, College Station
Date: Wed, 14 Oct 1992 02:55:21 GMT

Jonathan Seldin writes:
  > Think of A if and only if B.  This is A <--> B; A if B is clearly
  > B --> A, and so A only if B must be A --> B.

The indicated argument is invalid:
----------------------------------------------------------------
	A if and only if B     is paraphrased as     A <-> B   
but	A if             B     is paraphrased as     B  -> A
hence	A        only if B     is paraphrased as     A  -> B
----------------------------------------------------------------
This is a "subtraction" argument that doesn't look too good.  If 
"A only if B" were correctly paraphrased as the biconditional, then 
"A if and only if B" and "A if B" could still be paraphrased as the 
premises indicate, but the conclusion would then be false.  Of course, 
it would then be redundant to say "if and only if" instead of just 
"only if", but so what?

  > Another way to think of this is in terms of truth table values.
  > In A only if B, the case that is excluded is that A is true and B
  > is false; A only if B is true (truth functionally) in all other
  > cases.  This gives us the truth table for A --> B.

This argument begs the question.  Anyone who thinks "A only if B" is 
a biconditional will reject your premise that the only excluded case 
is that A is true while B is false.  They will claim that another 
excluded case is that A is false while B is true.

Nonetheless, "A only if B" has to be paraphrased as  A -> B, not the 
biconditional, otherwise (1) would be a downright inconsistency.

(1)	John will dance only if Mary dances, and maybe not even then.

(The "maybe" is just an epistemic modality, not relevant here.)  
The consistency of (1) indicates that "only if" is not a biconditional 
connective, but (1) suggests that perhaps there is a cancelable 
implicature (not entailment) of the converse conditional.  So 
"A only if B" is paraphrased as "A -> B" if you think formal 
paraphrases should capture entailments but not implicatures, i.e., 
if the paraphrase should reveal a "logical form".

B-o} Michael
_______________________________________________________________________
-----------------------------------------------------------------------
Michael Hand                     phone (409)845-5660, fax (409)845-0458
Dept of Philosophy, Texas A&M Univ, College Station TX 77843-4237 U.S.A.
From: ard@cs.bham.ac.uk (Antoni Diller)
Newsgroups: sci.logic
Subject: Ideals and filters
Date: 7 Oct 92 09:45:20 GMT
Organization: School of Computer Science, University of Birmingham, UK

Could someone explain to me what the following are:

ideal, prime ideal, filter and ultrafilter;

in the context of model theory, I think.  (I asked this about two weeks ago
but then I had to go away and all email addressed to me had accidentally
been deleted.)  Replies by7 email preferred.


Antoni Diller
A.R.Diller@cs.bham.ac.uk
Newsgroups: sci.logic,sci.math,sci.philosophy,sci.philosophy.meta,sci.physics,sci.ai.philosophy,comp.theory
From: rz@mips.complang.tuwien.ac.at (Richard Zach)
Subject: Kurt Goedel Society: EMailing List
Followup-To: poster
Reply-To: zach@csdec1.tuwien.ac.at
Organization: Technische Universit"at Wien
Date: Sun, 11 Oct 1992 17:33:45 GMT

                       KURT GOEDEL SOCIETY

                     Electronic Mailing List



The Kurt Goedel Society is setting up an electronic mailing list
for members and people interested in the activities of
the Society. Information about the Goedel Colloquia,
Calls for Papers, the Collegium Logicum Lecture Series,
the Newsletter, and information from sister societies
will be distributed. If you would like to be included
in the mailing list, or have any questions, send email to:

                    kgs@csdec1.tuwien.ac.at

The next Kurt Goedel Colloquium: Proof Theory and Computational Logic
will be held in August 1993 in Brno, Czech Republic.
From: frankt@cwi.nl (Frank Teusink)
Newsgroups: sci.logic
Subject: Re: A only if B
Date: 14 Oct 92 10:16:21 GMT

seldin@alcor.concordia.ca ( JONATHAN SELDIN ) writes:

[stuff deleted]

>Think of A if and only if B.  This is A <--> B; A if B is clearly
>B --> A, and so A only if B must be A --> B.

>Another way to think of this is in terms of truth table values.
>In A only if B, the case that is excluded is that A is true and B
>is false; A only if B is true (truth functionally) in all other
>cases.  This gives us the truth table for A --> B.

I agree totaly in the mathemathical sense. But I think that when
we use the phrase "only if" in language, the "if" part is often
implicite. I would not say "Tom will come only if we invite him",
if I thought that even with an invitation, Tom might not come.
This "if" part might even be considered stronger in the phrase
"Only if we invite him, Tom will come to diner". So, I think
that if you're interpreting a text, the `A <-- B' part should
follow immediatly, while one should somehow look more closely
whether or not `A --> B' is implicitely assumend.

>Jonathan P. Seldin
>Department of Mathematics                 seldin@alcor.concordia.ca
>Concordia University			   seldin@vax2.concordia.ca
>7141 Sherbrooke Street West, Montreal, Quebec, Canada, H4B 1R6

Frank Teusink
Newsgroups: sci.logic
From: pratt@Sunburn.Stanford.EDU (Vaughan R. Pratt)
Subject: Re: John Etchemendy
Organization: Computer Science Department,  Stanford University.
Date: Thu, 8 Oct 1992 03:52:23 GMT

In article <1992Oct7.065815.25425@klaava.Helsinki.FI> amnell@klaava.Helsinki.FI (Marko Amnell) writes:
>On an unrelated note, I have in front of me a new book by Etchemendy,
>_The Concept of Logical Consequence_.


Related to this is the paper by Fagin, Halpern, and Vardi, "What is an
inference rule?", in the current issue of J. Symbolic Logic, 57:3
1018-1045, Sept. 1992.  The paper introduces a general semantic
framework for exploring various meanings of "inference" ranging from
validity to truth inference.

-- 
=================================================== In short, I am floundering
Vaughan Pratt   pratt@cs.Stanford.EDU  415-494-2545 around and don't take what
=================================================== I say seriously.
Newsgroups: sci.logic
From: harding@mantaray.micro.umn.edu (Paul Harding)
Subject: Question about 'OR'
Organization: University of Minnesota CIS
Date: Fri, 16 Oct 1992 20:57:41 GMT
From: yodaiken@chelm.cs.umass.edu (victor yodaiken)
Newsgroups: sci.logic
Subject: Re: Russell's Paradox (was re: Of apples and their skins)
Date: 11 Oct 92 19:15:12 GMT
Organization: University of Massachusetts, Amherst

In article <1992Oct10.105913.9955@samba.oit.unc.edu> Robert.Vienneau@bbs.oit.unc.edu (Robert Vienneau) writes:
>In short, I find most engineers and mathematicians (!) are sleepwalking.
>They think there some's basis for their manipulations, and they think
>they know what they're doing. On the other hand, specialists in logic
>and set theory have been producing a century's worth of unreadable technical
>monographs showing that the practitioners have no understandable basis
>for their practice. Is something drastically wrong here? Am I right
>to feel uncomfortable? Is the current situation unsubstainable?

Most engineers and mathematicians use mathematical principles which may
be tested against observed reality, so they don't have to worry about
post-facto validation of their deductive methods.  The language
of mathematics, like other human languages, seems to elude simple reduction
to a set of axioms and mechanical productions.  Why should this 
distress anyone?

-- 


yodaiken@chelm.cs.umass.edu
Newsgroups: sci.logic,sci.math,comp.theory,sci.philosophy,sci.philosophy.meta,sci.physics,comp.ai.philosophy
From: frank@Cookie.secapl.com (Frank Adams)
Subject: Re: A only if B
Date: Mon, 12 Oct 1992 21:55:18 GMT
Organization: Security APL, Inc.

In article <rkaivola.718902434@mits> rkaivola@mits.mdata.fi (Risto Kaivola) writes:
>  Exactly how should one formalize the English notion of 'only if'
>in the language of the propositional calculus?
>  That is, given the sentence
>"Tom will visit us only if we invite him.",
>is the correct formalization
>
>A = "Tom will visit us."
>B = "We invite him."
>
>A  -->  B
>
>Or, should this perhaps be B --> A (not in my opinion), or A <--> B
>(this last alternative is more likely to be correct than B --> A, in my
>opinion)?

Right the first time.

B --> A would be "Tom will visit us if we invite him"; the "only" makes the
implication go the other way.

Note that mathematicians say "if and only if" (usually written "iff") for
A <--> B.  It can be argued that some actual instances of "A only if B" in
speech mean A <--> B, but I think a better interpretation in such cases is
A --> B, with the B --> A part being taken for granted.

The problem with A --> B is that we think of --> as representing *causal*
implication, which would mean "Because Tom will visit us, we will invite
him."  But the propositional implication does not have this meaning.
From: burt@aupair.cs.athabascau.ca (Burt Voorhees)
Newsgroups: sci.logic
Subject: Re: A only if B
Date: 13 Oct 92 16:23:16 GMT

>A-->B = if A then B
>A<-->B = A if and only if B
>A<--B = A only if B = if B then A  This is read: A is true only if B is
>true since a true statement cannot imply a falsehood.

  Appologies, this is clearly wrong. :(  That's what I get for posting
late at night and thinking about things like necessary and sufficient.
Guess that puts me one up on Dogwood (Much Ado About Nothing) as he only
wanted to be written down an ass.  :):):)
  Let's try again:  How about A only if B = (B-->A)&(-B-->-a)
bv
Newsgroups: sci.logic
From: seldin@alcor.concordia.ca ( JONATHAN SELDIN )
Subject: Re: A only if B
Summary: Correct is A --> B
Organization: Concordia University, Montreal, Quebec
Date: Tue, 13 Oct 1992 18:07:21 GMT

In article   writes:
...
>In article <rkaivola.718902434@mits> rkaivola@mits.mdata.fi (Risto Kaivola) writes:
>>
>>  The following is no doubt a little trivial for the participants of this
>>group, but I hope someone is willing to help me, nevertheless.
>>  Exactly how should one formalize the English notion of 'only if'
>>in the language of the propositional calculus?
...  (Formalization of A only if B requested.)
>>A  -->  B
... (blank lines omitted)
>>Or, should this perhaps be B --> A (not in my opinion), or A <--> B
>>(this last alternative is more likely to be correct than B --> A, in my
>>opinion)?
...
>>(Internet address:   rkaivola@mits.mdata.fi)
>
>I'd go for:
>
>(B --> A) & (-B --> -A)
>
>
>Antoni Diller

No!!!

Think of A if and only if B.  This is A <--> B; A if B is clearly
B --> A, and so A only if B must be A --> B.

Another way to think of this is in terms of truth table values.
In A only if B, the case that is excluded is that A is true and B
is false; A only if B is true (truth functionally) in all other
cases.  This gives us the truth table for A --> B.

So rkaivola@mits.mdata.fi was right the first time.

-- 
Jonathan P. Seldin
Department of Mathematics                 seldin@alcor.concordia.ca
Concordia University			   seldin@vax2.concordia.ca
7141 Sherbrooke Street West, Montreal, Quebec, Canada, H4B 1R6
Newsgroups: sci.logic
From: cmenzel@tamsun.tamu.edu (Chris Menzel)
Subject: Re: The Mathematical Universe
Organization: Texas A&M University, College Station
Date: Tue, 13 Oct 1992 21:31:59 GMT

In article <1992Oct13.191930.17813@guinness.idbsu.edu> holmes@opal.idbsu.edu (Randall Holmes) writes:
>Michael Hand writes:
>>  ...[T]here is little to conclude except that any feature of an account
>>  that identifies 3 with a set is a superfluous one -- and that therefore
>>  3, and its fellow numbers, could not be sets at all.
>>
>>  [from "What Numbers Could Not Be"]
>>_______________________________________________________________________
>>-----------------------------------------------------------------------
>>Michael Hand                     phone (409)845-5660, fax (409)845-0458
>>Dept of Philosophy, Texas A&M Univ, College Station TX 77843-4237 U.S.A.
>  
>Au contraire, it is obvious which set the cardinal number 3 is.  It is
>the set of all sets with three elements (this _can_ be defined in a
>non-circular manner, by the way).  

Surely it is obvious that this set is *not* the cardinal number 3,
since otherwise, by extensionality, we get a different number 3
whenever something begins or ceases to exist--unless you want to say
that only pure sets (or at least sets of eternal objects) are elements
of the number 3, but that would introduce just the sort of
arbitrariness that gives Benacerraf's argument its bite.

Nonetheless, there *is* something very natural about the set you
identify with 3; maybe because it is the *extension* of a much more
plausible candidate (at least for the friends of intensionality),
viz., the *property* that all 3-membered sets have in common...

>The opinions expressed		|     --Sincerely,
>above are not the "official"	|     M. Randall Holmes
>opinions of any person		|     Math. Dept., Boise State Univ.
>or institution.		|     holmes@opal.idbsu.edu

--Chris Menzel
  Department of Philosophy
  Texas A&M University
From: holmes@opal.idbsu.edu (Randall Holmes)
Newsgroups: sci.logic
Subject: Re: The Mathematical Universe
Date: 15 Oct 92 19:33:38 GMT
Organization: Boise State University

In article <1992Oct13.213159.23649@tamsun.tamu.edu> cmenzel@tamsun.tamu.edu (Chris Menzel) writes:
>In article <1992Oct13.191930.17813@guinness.idbsu.edu> holmes@opal.idbsu.edu (Randall Holmes) writes:
>>Michael Hand writes:
>>>  ...[T]here is little to conclude except that any feature of an account
>>>  that identifies 3 with a set is a superfluous one -- and that therefore
>>>  3, and its fellow numbers, could not be sets at all.
>>>
>>>  [from "What Numbers Could Not Be"]
>>>_______________________________________________________________________
>>>-----------------------------------------------------------------------
>>>Michael Hand                     phone (409)845-5660, fax (409)845-0458
>>>Dept of Philosophy, Texas A&M Univ, College Station TX 77843-4237 U.S.A.
>>  
>>Au contraire, it is obvious which set the cardinal number 3 is.  It is
>>the set of all sets with three elements (this _can_ be defined in a
>>non-circular manner, by the way).  
>
>Surely it is obvious that this set is *not* the cardinal number 3,
>since otherwise, by extensionality, we get a different number 3
>whenever something begins or ceases to exist--unless you want to say
>that only pure sets (or at least sets of eternal objects) are elements
>of the number 3, but that would introduce just the sort of
>arbitrariness that gives Benacerraf's argument its bite.

Real objects are eternal (including the ones which appear to change).
Parmenides was one smart guy.  Think about chunks of 4-space...

>
>Nonetheless, there *is* something very natural about the set you
>identify with 3; maybe because it is the *extension* of a much more
>plausible candidate (at least for the friends of intensionality),
>viz., the *property* that all 3-membered sets have in common...
>

Which is exactly the same thing, if one identifies properties with
their extensions, as I do...

>>The opinions expressed		|     --Sincerely,
>>above are not the "official"	|     M. Randall Holmes
>>opinions of any person		|     Math. Dept., Boise State Univ.
>>or institution.		|     holmes@opal.idbsu.edu
>
>--Chris Menzel
>  Department of Philosophy
>  Texas A&M University


-- 
The opinions expressed		|     --Sincerely,
above are not the "official"	|     M. Randall Holmes
opinions of any person		|     Math. Dept., Boise State Univ.
or institution.			|     holmes@opal.idbsu.edu
From: cavalcan@thomson-lcr.fr (Marcos Cavalcanti)
Newsgroups: sci.logic
Subject: Shoham's work
Date: 15 Oct 92 16:32:39 GMT
Organization: Thomson-CSF LCR, Orsay, France

]Newsgroups: sci.logics
Subject: Shoham's work
Summary: 
Followup-To: 
Distribution: world
Organization: Thomson-CSF LCR, Orsay, France
Keywords: 

Does anyone know of any papers (articles, etc.) or comments about Shoham's 
work "Reasoning About Change: Time and Causation from the standpoint of AI", 
PhD Thesis, Yale, 1987 ???
Thank you!
Marcos Cavalcanti    Email: cavalcan@thomson-lcr.fr
Newsgroups: sci.logic
From: danco@titan.ucc.umass.edu (DANIEL F COHEN)
Subject: Re: A only if B
Organization: University of Massachusetts, Amherst
Date: Wed, 14 Oct 1992 23:09:58 GMT

In article <rkaivola.718902434@mits> rkaivola@mits.mdata.fi (Risto Kaivola) writes:

>  Exactly how should one formalize the English notion of 'only if'
>in the language of the propositional calculus?
>  That is, given the sentence
>"Tom will visit us only if we invite him.",
>is the correct formalization
>A = "Tom will visit us."
>B = "We invite him."
>A  -->  B


Exactly.  The only assignment of truth-values which makes 'A only if B' false
is when A is true and B is false.  Same truth value assignments as A->B.

--Dan
From: sasghm@theseus.unx.sas.com (Gary Merrill)
Subject: Re: A only if B
Originator: sasghm@theseus.unx.sas.com
Date: Mon, 12 Oct 1992 18:55:33 GMT
Organization: SAS Institute Inc.


In article <Bw0r39.G2I@cs.bham.ac.uk>, ard@cs.bham.ac.uk (Antoni Diller) writes:
|> In article <rkaivola.718902434@mits> rkaivola@mits.mdata.fi (Risto Kaivola) writes:

	[ stuff about translating conditionals deleted ]

Here are the usual translations found in logic texts for the material
(and similar) conditional and biconditional:

     --------------------------------------------

     P -> Q

     if P then Q
     if P, Q
     Q if P
     Provided that P, Q
     Q provided that P
     On condition that P, Q
     Q on condition that P
     P only if Q
     P only on condition that Q

     ---------------------------------------------

     P <-> Q

     P if and only if Q
     P just in case Q
     P when and only when Q
     P exactly on condition that Q

     -------------------------------------------

There are probably other common translations as well, but I
cannot recall at the moment.

For some reason 'only' tends to confuse people (I suspect it
is because they don't really know how it works in English).
Sometimes it is easier to get the correct sense of an 'only'
expression by considering a quantified version, as in

	Only a dog is a labrador retriever.

	(x is a labrador retriever) -> (x is a dog)

	Bob is a labrador retriever only if he is a dog.

On the other hand, in my experience, many people find this
even *more* confusing.  In reading 'P->Q' as 'P only if Q'
it helps to emphasize the 'only':  P *only* if Q.  (If you
say the 'only' loudly enough you start to get the idea.)

-- 
Gary H. Merrill  [Principal Systems Developer, C Compiler Development]
SAS Institute Inc. / SAS Campus Dr. / Cary, NC  27513 / (919) 677-8000
sasghm@theseus.unx.sas.com ... !mcnc!sas!sasghm
Newsgroups: sci.logic
From: e343mh@tamuts.tamu.edu (Michael Hand)
Newsgroups: sci.logic
Subject: Re: The Mathematical Universe
Date: 9 Oct 92 20:36:58 GMT
Article-I.D.: tamsun.1992Oct9.203658.25387
Organization: Texas A&M University, College Station

Randall Holmes and Chris Menzel write:

Holmes> I also maintain that the physical world is a "mathematical object".

Menzel> I take it you don't think the physical world is *literally* a 
      > mathematical object, if only for the fact that, as you yourself 
      > hint, any number of other mathematical objects would have served 
      > just as well.

Holmes> Indeed many other objects would have served as well (do in
      > fact serve as well?); our position makes it impossible to discover
      > which one has in fact served :-)

Recall Benacerraf on a similar skepticism + absurd ontological 
identification (namely, identifying numbers with certain sets 
instead of certain others, much as Holmes identifies the world
with a certain mathematical object instead of another that would
serve as well); the application to Holmes's view is obvious.
I also recommend that anyone interested in attacking Benacerraf
on this issue read his paper instead of reacting just to these
suggestive quotes.

  If the numbers constitute one particular set of sets, and not another, 
  then there must be arguments to indicate which...

  In awaiting enlightment on the true identity of 3 we are not awaiting a 
  proof of some deep theorem.  Having gotten as far as we have without 
  settling the identity of 3, we can go no further.  We do not know what a 
  proof of that *could* look like.  The notion of "correct account" is 
  breaking loose from its moorings if we admit of the possible existence 
  of unjustifiable but correct answers to questions such as this...

  ...[T]here is little to conclude except that any feature of an account
  that identifies 3 with a set is a superfluous one -- and that therefore
  3, and its fellow numbers, could not be sets at all.

  [from "What Numbers Could Not Be"]
_______________________________________________________________________
-----------------------------------------------------------------------
Michael Hand                     phone (409)845-5660, fax (409)845-0458
Dept of Philosophy, Texas A&M Univ, College Station TX 77843-4237 U.S.A.
From: sasghm@theseus.unx.sas.com (Gary Merrill)
Newsgroups: sci.logic
Subject: Re: The Mathematical Universe
Keywords: inconsistent multiplicities
Date: 7 Oct 92 14:12:50 GMT
Organization: SAS Institute Inc.
Originator: sasghm@theseus.unx.sas.com


In article <1992Oct6.155930.2363@guinness.idbsu.edu>, holmes@opal.idbsu.edu (Randall Holmes) writes:

|> Where I do find talk of possible worlds reasonable is in the
|> discussion of the physical world that we live in.  Since I think that
|> the physical world is a subset of the logical universe, I find it
|> reasonable to suppose that alternate physical worlds (all possible
|> ones) _actually exist_ (in exactly the same sense that ours does).

It's this "same sense" that bothers me a bit.

Can I get to another one of them?  How?  Or am *I* already in (some of)
them?  Is it really *me*?  Can we communicate with the populations of
these possible worlds (as we can with the populations of our own)?

|> Such worlds provide an actual model for Kripke's semantics for modal
|> logic, for discussions restricted to the physical world; in the
|> internal language of this model, they are "possible worlds".  It is
|> probably an abuse of terminology to call them "possible worlds"
|> without reference to this model.  I don't think that one of them is
|> especially worthy of notice, except for the fact that I (and all of
|> _us_) are in it.

But isn't this a big "except"?  As in "The difference between P and -P
is not worthy of notice except for the fact that P is true and -P is
false"?

|> In an absolute sense (relative to the _logical_ universe) I am _not_ a
|> possible worlds realist; I think that there is one actual logical
|> universe.  However, there are various ways to describe the actual

I think the word "actual" is then a no-op here.  What is its sense?










-- 
Gary H. Merrill  [Principal Systems Developer, C Compiler Development]
SAS Institute Inc. / SAS Campus Dr. / Cary, NC  27513 / (919) 677-8000
sasghm@theseus.unx.sas.com ... !mcnc!sas!sasghm
Newsgroups: sci.logic