The Logic Forum Discussion Area

Logic
This Forum is Locked
Author
Comment
View Entire Thread
Re: FUTURE LOGIC - Comments & Queries

Hi JayDee, in reply to your question.
When two propositions are contrary it means that they cannot be both true, but may be both false.
In the case of seven (or any set of three or more) propositions, we can well say that more than one of them cannot be true, but still at least one of them must be true (i.e. they cannot be all false).
That 'only one of them can be true' does not exclude that 'one of them must be true'.
This holds, notice, even if you take any two at random and say that they are contrary to each other, i.e. that the pair may be both false.

Something about you (optional) logician-phil.osopher

Re: FUTURE LOGIC - Comments & Queries

Thanks Avi, I guess I'm still a bit confused. If the relations (propositions) are mutually exclusive and exhaustive I understand that to mean that for any pair of propositions, one and only one of the relations *must* be true. Am I wrong?

By "exhaustive" I mean as fits the definition as given on page 25 and in table 3.1. Here, nonP + nonQ is logically impossible, but in table 6.1 it isn't (although "contrariety" isn't the same as "exhaustive").

It seems to me that the relations (taken as a set) are contradictory and not contrary because they are mutually exclusive, meaning if one is true then the others must be false, and also since one must be true then they cannot all be false. I.e., a "no" under columns P+Q and nonP+nonQ (which meets the criteria of contradictory).

I understand your point that 'only one of them can be true' does not exclude that 'one of them must be true', but isn't the issue rather that they cannot all be false?

Re: FUTURE LOGIC - Comments & Queries

The logic of oppositions is best understood by matrix analysis.
In the case of two propositions, the matrix is:
1) P + Q
2) P + notQ
3) notP + Q
4) notP + notQ
These are the 4 general, prima facie, logical possibilities for two propositions.
If the propositions are shown to be contradictory, it means that the alternatives 1 and 4 are impossible, while the alternatives 2 and 3 are possible. If the propositions are contrary, then the alternative 1 is impossible, but the other three are possible. If the propositions are subcontrary, then the alternative 4 is impossible but the otherr three are possible. And so on.
Now when you deal with three or more (e.g. seven) propositions, obviously the matrix is going to be accordingly larger, with more alternatives, and more ways they might be combined. For instance, with three propositions we have:
P + Q + R
P + Q + not R
P + notQ + R
notP + Q + R
and so on... till notP + notQ + notR (this is given in full in the book somewhere).
That's how we know we have exhausted the logical possibilities - by listing them all.

Something about you (optional) logician-phil.osopher

Re: FUTURE LOGIC - Comments & Queries

Thanks Avi, I guess I'm still a bit confused. If the relations (propositions) are mutually exclusive and exhaustive I understand that to mean that for any pair of propositions, one and only one of the relations *must* be true. Am I wrong?

NOT WRONG. THIS IS THE DEFINITION OF CONTRADICTION (NOT CONTRARIETY).

By "exhaustive" I mean as fits the definition as given on page 25 and in table 3.1. Here, nonP + nonQ is logically impossible, but in table 6.1 it isn't (although "contrariety" isn't the same as "exhaustive").

YES, EXHAUSTIVE MEANS THE NEGATION OF ALL THE PROPOSITIONS IS IMPOSSIBLE. MUTUALLY EXCLUSIVE MEANS THE AFFIRMATION OF ALL THE PROPOSITIONS IS IMPOSSIBLE.

It seems to me that the relations (taken as a set) are contradictory and not contrary because they are mutually exclusive, meaning if one is true then the others must be false, and also since one must be true then they cannot all be false. I.e., a "no" under columns P+Q and nonP+nonQ (which meets the criteria of contradictory).

THIS WORKS WITH TWO PROPOSITIONS, WITH THREE OR MORE PROPOSITIONS THERE ARE MORE POSSIBILITIES, AS IS CLEAR WITH REFERENCE TO MATRICES.

I understand your point that 'only one of them can be true' does not exclude that 'one of them must be true', but isn't the issue rather that they cannot all be false?

ONE MUST BE TRUE MEANS THE SAME EXACTLY AS THEY CANNOT ALL BE FALSE. IN SOME CASES, ONLY ONE CAN BE TRUE. IN OTHERS, MORE THAN ONE MIGHT BE ALLOWED TO BE TRUE (UP TO ALL BUT ONE).

Something about you (optional) logician-phil.osopher

Re: FUTURE LOGIC - Comments & Queries

Ok, thanks Avi, sorry about the confusion.

Do these relations hold for ALL the forms of proposition which are covered in the book? (categorical, modal, conditional, etc).

I notice that the unconnectedness relation has no column in which a pair of propositions is not possible. Would it be true to say that in general, the "strength" of a relation is correlated (positively) with the number of impossible combinations? So the strongest relations are implicance and contradiction, each having two "no's", and the weakest is unconnectedness, which has none.

Re: FUTURE LOGIC - Comments & Queries

Hi JD,

Do these relations hold for ALL the forms of proposition which are covered in the book? (categorical, modal, conditional, etc).

THE LISTED OPPOSITIONS (CONTRADICTION, CONTRARIETY, ETC.) ARE OBVIOUSLY APPLICABLE TO ANY PAIR OF PROPOSITIONS OF ANY SORT, IN THIS BOOK OR ANY OTHER. THEY ARE JUST EXTENSIONS OF THE THREE LAWS OF THOUGHT.

I notice that the unconnectedness relation has no column in which a pair of propositions is not possible. Would it be true to say that in general, the "strength" of a relation is correlated (positively) with the number of impossible combinations? So the strongest relations are implicance and contradiction, each having two "no's", and the weakest is unconnectedness, which has none.

YES, THAT IS CORRECT. THE MORE COMBINATIONS ARE IMPOSSIBLE, OBVIOUSLY THE STRONGER THE 'OPPOSITION' RELATION BETWEEN THEM.

JD, keep in mind that the named oppositions refer to PAIRS of propositions. When dealing with sets of 3, 4, 5, 6, etc. propositions, the different possibilities of 'impossible' and 'possible' rows are ALSO 'oppositions', except that we have not given them any specific names because that would require a never-ending vocabulary! Instead we resort to descriptive sentences like "one of them must be true" or "all but one of them must be false" etc. All this, to repeat, is merely application of the laws of thought.

Something about you (optional) logician-phil.osopher

Re: FUTURE LOGIC - Comments & Queries

Avi
Hi JD,
JD, keep in mind that the named oppositions refer to PAIRS of propositions. When dealing with sets of 3, 4, 5, 6, etc. propositions, the different possibilities of 'impossible' and 'possible' rows are ALSO 'oppositions', except that we have not given them any specific names because that would require a never-ending vocabulary!


Thanks Avi. Noted!

Re: FUTURE LOGIC - Comments & Queries

I've spotted a couple of typos in the book, they're not serious but thought I'd mention them anyway.

page 6 (Table of Contents) : NATURALS CONDITIONALS... and the same for the corresponding title on page 209 (a superfluous 's' on the end of 'NATURAL').

page 41 (bottom) : 'Although these may [be] tedious details...'

If I see any more I'll post them here.

Re: FUTURE LOGIC - Comments & Queries

Hi algojack. Thank you very much. Yes, if you spot any errors, I will correct them. Cheers, Avi.

Something about you (optional) logician-philosopher

Re: FUTURE LOGIC - Comments & Queries

Hi Avi,

In FL Part 1 you discuss plural categoricals and singulars where only the subject term is singular, but not what you might call "double" singulars where the predicate is also a singular. E.g.

Paris is the capital of France

Is this a deliberate oversight because that form is too trivial to mention? I suppose technically they are not even syllogisms, maybe that's why you haven't included them. Just wondered...

Re: FUTURE LOGIC - Comments & Queries

Hi MDB. I do not remember if I mention singular predicates anywhere and deal with it. Thanks for the remark. Some offhand comments:

Various forms (with copula is) are conceivable. If the predicate is singular, and the proposition positive, the subject will be singular (or a list of singulars). But in a negative proposition with a singular predicate, the subject might be plural (e.g. no Asian city is Paris).

Obviously, a singular-singular proposition is convertible (to the same polarity), whether positive or negative.

In syllogism, the middle term can in such case be singular, either as subject in the major and predicate in the minor (1st fig.), or as predicate in both premises (2nd), or as subject in both premises (3rd), etc.

I let you work out the valid moods (according to the polarities involved), and share your findings with us. It should be a good exercise for you.

Best regards, Avi

Something about you (optional) logician-philosopher

Re: FUTURE LOGIC - Comments & Queries

Ok Avi, I will do what you suggest and post my results here over the weekend.

Most books on Logic treat singulars as universals, so Socrates is a man would be put into the form All S is M. You do mention in FL that this is essentially the case. This being so, is there any particular reason why you have included separate propositions R & G and their analyses?

Re: FUTURE LOGIC - Comments & Queries

Yes, it is very useful to engage in theoretical research yourself - nothing sticks better in the mind than that. Become a logician yourself.

Yes, singular-singular are like universals but not exactly. This is most true of a negative proposition (like no x is y). A positive proposition would have the joint value of two universals (like all x are y and all y are x), since it is also convertible. The issue here is playing the role of middle term...

Actually, modern logicians have given these forms much attention. But I didn't for lack of time (at the time). I believe (like most) that all propositional forms deserve attention, however.

The ordinary singulars R and G are very valuable. I introduced these symbols in FL (from affiRmo and neGo), because I perceived the need. Since then, I have also seen the value of this deed in later works.

Another small innovation in FL was the introduction of two more oppositional relations Implicance (mutual implication) and Unconnectedness (none of the five other relations). I mention this because I've recently seen a number of works which mention this innovation of mine as if it was a voluntary thing, and wonder why I did it. No - it is essential to have a complete list of all possible relations to work with (and not just the traditional four - contradiction, contrareity, subcontrareity, and subalternation). Also subalternating is different from being-subalternated. As you proceed through FL (and other works), you'll see these oppositional relations are all useful.

In The Logic of Causation, notably, the issue of opposition becomes still more complex, with the realization that there are conditional oppositions. Two propositions may be unconnected prima facie, but they may turn out to have some sort of (positive or negative) connection under specific conditions...

Something about you (optional) logician-philosopher

Re: FUTURE LOGIC - Comments & Queries

Ok, here is my attempt to find the valid syllogisms for singular-singular propositions. I have named them R2 and G2, following the standard singulars:

R2 : This S is this P
G2 : This S is not this P

So altogether there are 8 x 8 = 64 possible premises for each figure. However, since R2 and G2 are both convertible, isn't it the case that results for any one figure will apply to all? Anyway, I'll just give the results for the first figure.

Premises involving the plurals can be discounted since there will be no connection, which leaves just the following 7 (ignoring those in which the premises are the same but the order is different):

R,R2
R,G2
G,R2
G,G2
R2,R2
R2,G2
G2,G2

And here are the full syllogisms:

R This M is P
R2 This S is this M
con This S is P

R This M is P
G2 This S is not this M
con NONE

G This M is not P
R2 This S is this M
con This S is not P

G This M is not P
G2 This S is not this M
con NONE

R2 This M is this P
R2 This S is this M
con This S is this P

R2 This M is this P
G2 This S is not this M
con This S is not this P

G2 This M is not this P
G2 This S is not this M
con NONE

So there are only 4 valid syllogisms (first figure):

R R2 R
G R2 G
R2 R2 R2
R2 G2 G2

I may return to the other figures later, but for now I'm keen to continue on to part II of the book. Hopefully I haven't completely messed up!

Re: FUTURE LOGIC - Comments & Queries


So altogether there are 8 x 8 = 64 possible premises for each figure.


This should have been 64 possible pairs of premises, of course.

Re: FUTURE LOGIC - Comments & Queries

Hi MDB, well done, but you missed one valid mood.


Not so interesting are the moods you listed with a plural major term (P). To be thorough, you need to also look into moods with a plural minor term (S) (I mention a negative example higher up - No Asian city is Paris ... a positive example would be ?). Let's just focus for now on the fully singular syllogisms.

sing-sing syllogs:

Let S, M, P be three singular terms (or this S, this M, this P, as you have it) (e.g. the present capital of France, the location of the Eiffel Tower, Paris or Vienna). We have three out of four valid moods in the first figure.

M is P
S is M
S is P – valid

M is not P
S is M
S is not P – valid
(You missed this one)

M is P
S is not M
S is not P – valid

M is not P
S is not M
No conclusion

The most interesting mood here is of course the third one, because it has a negative minor premise and yet is valid, which is atypical/exceptional. For this mood alone it was worth looking into.

Let us compare this mood to plural syllogism. If the major premise was compound, with both directions universal, then the conclusion would be valid, because a 2nd fig. syllogism would actually be operative (not really the 1st fig. one).

(All M are P and) All P are M
No S is M
conclusion No S is P is valid

So that's why the sing-sing version works, really.

Regarding the other 3 figures, as you say, we just need to convert the major premise (2nd fig.) or the minor premise (3rd fig.) or switch the premises (4th fig.). Since all these propositions are fully convertible, there will be 3 valid moods out of 4 in each figure.

Something about you (optional) logician-philosopher

Re: FUTURE LOGIC - Comments & Queries

Avi, thanks for the feedback.


M is not P
S is M
S is not P – valid
(You missed this one)

M is P
S is not M
S is not P – valid


Aren't these essentially the same? I did have both on my list but discarded one because it's just a repeat of the other with Major/Minor premises reversed. This isn't the same as saying that in the plural syllogisms (fig. 1), EAE is the same as AEE, because the latter is invalid, but with singular-singular syllogisms both terms are the same from a distribution point of view. i.e. S is P = P is S and S is not P = P is not S. What am I missing?

Re: FUTURE LOGIC - Comments & Queries

Hi MDB.

If you switch 1st fig. premises you get a 4th fig. syllog. BUT the term symbols S and P must be changed.

P is M
M is not S
S is not P – valid

P is not M
M is S
S is not P – valid

As discussed in FL, and as Aristotle considered, the 4th fig. is somewhat artificial, not so natural a movement of thought as the other figures. But still, in some cases it brings an interesting conclusion not otherwise evident.

As regards the 1st fig. valid mood with a negative minor premise, as I said before it is unusual for a 1st fig. syllog. to so behave - and the explanation is given by me with reference to the 2nd. fig. in my previous post.

Something about you (optional) logician-philosopher

Re: FUTURE LOGIC - Comments & Queries

Avi, with regard to chapter 15, section 3 (validations), I'm having a hard time convincing myself that pnp in the 1st figure is invalid, although I've taken on board your comments on it.

I've tried comparing it with the 3rd fig. pnp, which is valid, but it's still not clear to me how the differences make one valid and the other invalid.

e.g. an invalid mood in pnp (1st fig.) would be:

All M can be P (p)
All S must be M (n)
therefore, All S can be P (p)

Rephrasing in terms of "circumstances", this would be

In some circumstances all M is P
in all circumstances all S is M
therefore in some circumstances all S is P

I'm trying to come up with suitable concepts for the terms which makes this syllogism intuitively invalid, but so far haven't been able to. Any suggestions?

Re: FUTURE LOGIC - Comments & Queries

Hi MDB,

In the first figure, the 'all circumstances' of the minor premises are those applicable to the minor term S, they are not all circumstances concerning the middle term M. For this reason, there is no guarantee that the 'some circumstances^concerning M in the major premise are covered.

On the other hand in the third figure, M being the subject in both premises, you can be sure of overlap of circumstances.

Best, Avi.

Something about you (optional) logician-philosopher

Re: FUTURE LOGIC - Comments & Queries

Thanks Avi, for some reason I just wasn't getting it. I think I was confusing myself by reading the premises as "all S in all circumstances is what P is in some circumstances". I was looking at the quantity and not the modality. Then I drew a diagram to represent the circumstances "surrounding" the terms. Being more of a visual thinker, the invalidity then became clear.

But still, some of these modal syllogisms aren't at all obvious.

Re: FUTURE LOGIC - Comments & Queries

In fig. 1, if you tried converting the minor premise, you would have immediately seen that while S was distributed, M was not. All S must be M converts to Some M can be S. Remember All S means: Each S - it is distributive, not collective or collectional. So, the all circumstances are all circumstances concerning each S, which are not the same set of circumstances... The universal proposition is a mere summary formula.

Note additionally that in the past, some logicians thought that a universal potential major premise in the first fig. could yield a valid conclusion. They did not realize the issues involved. So, you are in good company!

Something about you (optional) logician-philosopher