Formally, when you negate a quantified term which is attached to a relation, is a universal term always made particular and vice-versa?
For example, consider this statement :
Anyone who aids a criminal is immoral.
Where "anyone" is taken to mean "all persons" and "a criminal" is taken to mean "some criminal or other" (ie, a particular term).
Now the contraposition of the proposition is :
All moral persons fail to aid criminals.
Intuitively, we mean all criminals here (it would seem absurd to suggest that we're only talking about some criminals).
So what's happened is that the relation "aids" has been negated (it becomes "fails to aid", or more formally, "non-aids") and its object "criminal" has been transformed into a universal term.
The above seems correct but I have a doubt whether it applies in general. This could be because the quantity "any" is ambiguous; sometimes it can mean "all" and at other times "some".
e.g. the above proposition could have been expressed as :
Anyone who aids any criminal is immoral, where "any" means "some criminal or other".
and the contraposition could be expressed as :
All moral persons fail to aid any criminals, where in this case, "any" means "all".
I hope I've made myself clear and thanks in advance for any help.
Hi Joe. I would express the original proposition as "anyone who assists any criminal is immoral" and the contraposite as "A moral (i.e. not-immoral) person does not assist (i.e. is not one who assists) any criminal." Both subjects are universal, and the clause "any criminal" (distributive) retains its meaning.
Something about you (optional) logician-philosopher
Hi Avi,
Thanks for your input but I'm really looking for a general rule regarding negating quantified relational terms, ie one which works in all cases and doesn't depend on how the proposition is expressed.
Let me use another example:
All cats like some dogs
And obverting this proposition gives :
No cats dislike any (all) dogs
The two propositions have the same meaning.
So the rule seems to be :
When negating a relation and its object (e.g. "like some dogs"), negate the relation and if the object is distributed change it to undistributed and vice-versa.
I think this must be correct because not(all) = some and not(some) = all. We can see this from the traditional square of opposition and it shouldn't matter whether the term is attached to a relation or not.
Joe, here again, the relational aspect is incidental. "Every cat is [a creature that likes some dogs]" obverts to "No cat is not [a creature that likes some dogs]." The subject and predicate are really unchanged. The relational expression "likes" is really part of the predicate. So, no problem arises.
Something about you (optional) logician-philosopher
Hi Avi,
Given the following premises, is it possible to draw any conclusion?
1. Every owner of a dog is kind.
2. Some dogs are beagles.
Hi Joe. I'd say:
Every owner of a dog is kind
becomes:
All (owned) dogs have kind owners
Some dogs are beagles
should rather be stated as a general proposition:
All (owned) beagles are (owned) dogs
Now, we have a 1st figure syllogism AAA, with conclusion:
So, all (owned) beagles have kind owners
This can be restated as:
Every owner of a beagle is kind
Something about you (optional) logician-philosopher
I gave you the way to prove the desired conclusion. I added the owned to dogs and the owned to beagles and made the beagles proposition general.
Not all dogs or beagles have owners, of course.
If all you have is that some (owned) beagles are (owned) dogs, then the conclusion would be particular too, i.e. some owners of beagles are kind.
Something about you (optional) logician-philosopher
I should add, in case it is not obvious, that you cannot always get a conclusion from given premises. E.g. if your minor premise is really only that some dogs are beagles, you cannot be sure that the dogs that are beagles are owned, or that the beagles that are dogs are owned, and so you have no conclusion at all about owners of beagles.
As for my previous particular conclusion, viz. some owners of beagles are kind - come to think of it, that could still be every owner of beagles is kind, provided we understand that only beagles that are known to be dogs and owned are intended, since we are given that all owners of dogs are kind.
Your concern here and before is evidently with terms within terms. As shown here and above, the way to deal with these is to draw out the implicit propositions. But also to accept that in some cases, the desired conclusion is not possible.
Something about you (optional) logician-philosopher
Avi, this is how I would tackle it, but the correctness of the proof depends on "a dog" (undistributed) becoming "any dog" (distributed).
1. Every owner of a dog is a kind person. ("a dog" is undistributed)
2. Some dogs are beagles.
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3. Every unkind person is a non[owner of a dog], by (1), contraposition.
Now the predicate "non[owner of a dog]" when expanded out, so to speak, becomes
"a person who doesn't own any dog", where "dog" is now distributed. So (3) becomes
3. Every unkind person is a person who doesn't own any dog.
Now since we are talking about all dogs, we can substitute what is predicated of "some dogs" in premise 2, ie, beagles.
Thus :
4. Every unkind person is a person who doesn't own any beagle, by (2) and (3).
Finally, we can obvert (4) to get
5. No unkind person owns a beagle.
Where in (5) "doesn't own" has been contradicted to get "owns" and "any beagle" has been changed back from distributed to undistributed.
You mention the process of substitution in your book "Future Logic". It seems to me that all mediate inference is based on it. The rules of the traditional syllogism are really just a special case of the more general principle of substitution.
Contraposition of All dog-owners are kind persons All not(kind person) are non(dog-owners). It is not dog that is distributed in the original subject, but dog-owners. The negative term non(dog-owner) means not any dog-owner. A dog-owner in either case is an owner of some dog (dog undistributed).
Given your ONLY two premises, all dog-owners are kind and some dogs are beagles, you cannot draw the desired conclusion by substitution or any other means, for reasons already explained.
Non(dog-owner) cannot be changed to non(beagle-owner), because according to your statement, only some beagles are dogs (i.e. you refused all beagles are dogs). You cannot be sure that the beagles you have in mind are the dog variety, and therefore you cannot place the term beagle in lieu of the term dog.
Something about you (optional) logician-philosopher
Joe, sorry to disappoint you. But so far you have not managed to convince me. I'm not taking any line - I'm open-minded. But so far you have not shown me a convincing proof. Try formulating your thesis without dogs and beagles and without owners. Just symbols A, B, C, etc. for the terms, but still in ordinary language for the rest of it. You will, I wager, see for yourself that it can't be done.
One more comment I can make is that you do not realize that the negation of a complex term of the sort you have put forward is broader than you conceive. For example, the negation of [a creature that likes some dogs] is not [a creature that dislikes all dogs] - for it includes all other things in the universe. Or to put it differently, or more narrowly, not to like is not to dislike, because there is a third alternative, viz. indifference. Similarly with your other terms.
Something about you (optional) logician-philosopher