An introduction to formal logic

More scholastic material

The modern way of validating a syllogism is with the use of Venn Diagrams, and there are some good web sites that show how to use them, but in the spirit of the middle ages, I'll present the traditional method.

The traditional syllogism has three statements and three terms (Subject, Middle, and Predicate).

The conclusion is of the form Subject / operator / Predicate
Premise 1 relates the middle and predicate terms,
Premise 2 relates the middle and subject,
the conclusion relates subject and predicate.

There are four Figures:

1. Middle / Predicate
Subject / Middle
Subject / Predicate

2. Predicate / Middle
Subject / Middle
Subject / Predicate

3. Middle / Predicate
Middle / Subject
Subject / Predicate

4. Predicate / Middle
Middle / Subject
Subject / Predicate

We have a concept of "distribution". The members of a class are distributed according to the type of proposition, as follows:

"All" distributes the subject of a proposition.
"None" distributes the subject and predicate.
"Some" distributes neither subject nor predicate.
"Some - not" distributes the predicate (well, not in the sense of the other three, but you just have to accept this)

Distribution, with the exception of type O, thus says something about all members of a class. There are problems with this bald characterization, but you just have to trust me. :)

Now, four rules for validity (assuming non-empty classes):

Middle term distributed at least once
If a term is distributed in the conclusion, it must be distributed in a premise
At least one non-negative (A or I) premise
If the conclusion is negative (E or O) there must be a negative premise

Example 1 - :

All A are B
All C are A
All C are B

Known as Barbara. A is the Middle term, B the predicate and C the subject. All the valid figures have traditional names, the vowels of which correspond to the operators in the statements.

I never showed why this was valid did I?

A, the middle term, is distributed in premise 1. C is distributed in the conclusion, and in premise 2. Affirmative premises and conclusion. Valid.

This is of course an instance of the well-known

All men are mortal
All Greeks are men
All Greeks are mortal (or is that "all greeks are Socrates" - I forget)
 
Soubrette said:
Bill

I can understand your frustration but this is one thread surely which is actually not being hijacked - it may have gone down a road not intended by the a_u_p but it did so almost immediately, there was no attempt to police the thread by a_u_p so I can only assume the slight detour was ok by him.

So the irony is that it is you and I that appear to be thread jacking

Sou

Like there is something I can do to stop him? I had part of the question answere, which I was happy about, and it is finally getting back to the original topic, so I am starting to read it again. I don't think it was a slight detour, or a detour into an area of equal interest, which is something that often happens in a thread, but which I don't mind.
 
whitefork said:
(this is not an attack on anyone)


This is well-formed, but the so-called MIDDLE TERM (Muslims) is not "distributed" among subject and predicate. Venn diagrams (the "Ballentine Ale" symbol - 3 overlapping circles) would show this clearly but I don't know how to put them up here. What is means is that the set which is the intersection of Saudis and Terrorists may be null under the premisses (point being, all the terrorists, may in fact be non-saudis under the premisses).


You need to be in enhanced mode, then a magic 'attach file' option appears.

Venn diagrams i understand, I did them in year seven maths.
 

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BillHoyt said:

Point taken, Sou,

So let us ask A_U_P. DId this conversation get hi-jacked? Did you not want to find out about logic? Were Franko's posts on your point, or did they detract from them?

Has this thread been hi-jacked?

And, sou, look at the fallacy of compositon thread. Franko and hammy openly congratulate themselves on that hi-jacking.

Cheers,

Gee, I gave up on this thread ages ago, and have only just got back into it. Maybe we should start up not just a Franko thread, but a Franko forum. Then it should be pretty easy to keep out of his way.
 
whitefork said:
23 years IBM mainframe systems, assembler, COBOL, REXX, CICS, IDMS.

And you? Visual Basic, I recall.

About that truth table?


CICS, did you pronounce it C.I.C.S, like the traning videos, or KICKS, like we all did. That product caused us more trouble than anything else I have come across. Letting cobol programmers loose on unprotected memory is like giving babies razor blades to play with.

CICS joke.

Name two films stars and a dog.

Benji, Lassie and CICS.
 
whitefork said:
Ever try teaching an intro to logic course to freshmen at Ohio State? (oh, the pain)

You are of course correct....

An speaking of "Oh the pain" Doctor Smith of "Lost in Space" - Jonathan Harris - died.

"Danger, Will Robinson"....

Talk about hijacking threads, that guy hijacked a whole TV series. They orinally wanted him around for a couple of shows at the start to get it moving, then made himself indispensible. It would never have been half the show it was without him.

Apparently, he was also improvising his part, and after the initial shock, they realised he was on to something.
 
Hey Phineas!

Nice to see you back. I'm having fun with this, but all the research has brought back the dreaded "final exam" dreams.

CICS - the Canadians and Brits say Kicks, I used to say see-eye-see-ess, but they renamed it Transaction Server a few years back. It's a whole lot more stable than it was back in the 80's, but since my business is performance and stress testing, we find all sorts of opportunities for mayhem. Nobody should be working in that environment unless they have a few years of rigorous programming experience. That said, it's pretty much the only game in town for dealing with huge masses of data and very large transaction volume. (there's room for other opinions, but I'm an IBM mainframe bigot).

Thanks for the attachment tip.
 
Back to the syllogism

The first line of the poem: "Barbara celarent darii ferio que prioris"

Next in figure 1 is Celarent

No A are B
All C are A
No C are B

Middle (A) is distributed, C and B are distributed in the conclusion and the premisses, negative conclusion with negative premise.

Darii (see how this is going?)

All A are B
Some C is A
Some C is B

Ferio

No A is B
Some C is A
Some C is not B

Middle (A) distributed, predicate (B) distributed in conclusion and premise 1.

Completing the valid syllogisms in figure 1. With four figures, and four operators taken three at a time, we have I believe 256 different possible syllogisms, only a small number of which are valid.

Figure 2: Cesare camestres festino baroco secundae

Now it's a little more interesting, because the names contain mnemonics for transformation rules.

Cesare

No A are B
All C are B
No C are A

The "s" in Cesare is an instruction to convert the first premise (switch the subject and predicate). Conversion is a valid rule of inference for type E and I propositions, but not, of course for A and O (think about it: if no A are B, then no B are A, and if some A is B then some B is A. But if all A are B, then it's not necessary that all B are A)

After conversion, we get

No B are A
All C are B
No C are A

which is the same structure as Celarent.

Camestres

All A are B
No C are B
No C are A

The "m" says "change the order of the premisses", and the "s" says "convert" (since there are two, convert a premise and the conclusion)

After transposing:

No C are B
All A are B
No C are A

After conversion

No B are C
All A are B
No A are C = Celarent

Festino

No A are B
Some C is B
Some C is not A

again, conversion gives

No B are A
Some C is B
Some C is not A = Ferio

(Imagine a room full of wise guys like Hamlet being force-fed this material)

Baroco

All A are B
Some C is not B
Some C is not A

the "c" means reduction per impossibilis: That is, if we deny the conclusion, giving "All C are A", then by premise 1, and the validity of Barbara, we must conclude that "All C are B", contradicting premise 2. The validity of Barbara proves the validity of Baroco.

Notice that the first letter of the name indicates the syllogism of figure 1 to which the other figures reduce.

Figure 3: Tertia darapti disamis datisi felapton bocardo freison habet (Tertia is not a form, but means "third" - "habet" means "has")

Darapti

All A are B
All A are C
Some C are B

"P" means conversion per accidens, switching the subject and predicate, and changing the universal operator to the particular (A to I or E to O). Thus, All A is B becomes Some B is A, and No A is B becomes Some B is not A.

Thus
All A are B
Some C is A
Some C is B = Darii

Disamis

Some A is B
All A are C
Some C is B

Converting premise 1 and the conclusion (s twice) and transposing the premisses (m)

All A are C
Some B is A
Some B is C = Darii

(you wonder why they don't teach this anymore?)

Datisi

All A are B
Some A is C
Some C is B

Convert premise 2 (the s)

All A are B
Some C is A
Some C is B = Darii

Felapton

No A are B
All A are C
Some C is not B

Convert premise 2 per accidens (the p)

No A are B
Some C is A
Some C is not B = Ferio

Bocardo

Some A is not B
All A are C
Some C is not B

Per impossibilis (C) - Deny the conclusion giving All C are B. Then premise 2 and Barbara give All A is B, contradicting premise 1.

Ferison

No A are B
Some A are C
Some C is not B

Convert premise 2

No A are B
Some C are A
Some C is not B = Ferio

Figure 4: Quarta insuper addit Bramantip camenes dimaris fesapo fresison.

Bramantip

All A are B
All B are C
Some C are A

Tranpose premises (m) and (here's a bit of cheating) convert the conclusion of Barbara per accidens to get Some C are A

All B are C
All A are B
Some C are A = Barbara with converted conclusion

Camenes

All A are B
No B are C
No C are A

Transpose premises, convert conclusion

No B are C
All A are B
No A are C = Celarent

(just a few more, I'm on a roll here)

Dimaris

Some A is B
All B are C
Some C is A

Transpose premises, convert conclusion

All B are C
Some A is B
Some A is C = Darii

Fesapon

No A are B
All B are C
Some C are not A

convert premise 1, convert premise 2 per accidens

No B are A
Some C is B
Some C is not A = Ferio

(last one)

Fresison - I like this because it sounds dirty

No A are B
Some B are C
Some C are not A

convert both premises

No B are A
Some C are B
Some C are not A = Ferio

And now you know everything there is to know about the classical syllogism. (right).

If an argument does not fit one of these forms, then it requires "other methods" to demonstrate its validity (wink-wink)

Here endeth the lesson for the day.

I hope to continue by showing how some of these argument forms translate into Predicate logic, which is more in the Victor/LW line.
 
Re: Re: Back to the syllogism

a_unique_person said:


Are these all just stating the permutations and combinations of that venn diagram you were referring to?

What we have are four basic syllogisms of the first figure (Barbara, etc). That's the first line of the poem. (I will see about putting up the corresponding Venn diagrams). The other three lines are the mnemonic rules for transforming the syllogisms of the other three figures into those of figure one.

They're rules of inference, if you will.
 
Venn Diagrams

Barbara: All B are C, All A are B, therefore all A are C. The shaded areas have no members.
 
Baroco:

All A are B
Some C is not B
Some C is not A

The X is in a position within C that is not within B. Since all A is void except where it overlaps B, that X must outside of A's domain.

From these two example you should be able to guess at the others. The reduction of syllogisms to figure 1 does not imply that their Venn diagram representations are the same.
 
I'd suggest a rigorous treatment in terms of set theory, I guess. (which I am not in a good position to provide - it's been a while). Given a universe consisting of three sets A, B and C, you have the intersection of not-A and B null, not-B and C null, so the only members of A must remain in the intersection of A, B and C, so all the members of A are also members of C.
 
transition to predicate logic

the first time I heard the word logic was from my father who is a highly contentious man and likes to argue like nobody's business. Of course I have very little in common with him. He said once apropos of nothing "All squares are rectangles, but not all rectangles are squares". I don't remember how old I was at the time.

this sort of wisdom stays with you for a long time. Let us try to apply it.

In sentential logic we have propositions, which are either true or false. We can determine the truth value of a complex proposition by analysis. Predicate logic allows us to represent complex categorical propositions symbolically (lot of syllables there).

For instance, All A are B.

the universe consists of a lot of "x" and other funny letters. They are in lower case. Properties are represented by upper case letters like A, B, etc.

(x)(IF Ax Then Bx) - would be read as "If anything is A, then it is B" - the symbol - (x) - meaning "for every x". This does not mean that an x satisfying the condition "Ax" actually exists.

"All the Samoan Cy Young winners are bald" is a true statement.

But take this: "Some Samoan Cy Young winner is bald." This statement is symbolized as

(Ex)(Sx AND Bx) -- the "E" in "Ex" is supposed to be reversed -- .

that is, "there is at least one entity that is Samoan and a Cy Young winner AND that person is bald." A false statement.

So you have two operators, (x) and (Ex), the universal and existential quantifiers.

Barbara

All A are B
All C are A
All C are B

becomes

(x)(IF Ax Then Bx)
(x)(If Cx Then Ax)
(x)(If Cx Then Bx) the If - then being generally represented by a horseshoe symbol with open end to the left.

Celarent

No A are B
All C are A
No C are B

(x)(IF Ax then NOT-Bx) - if x is A then x is not B.
(x)(IF Cx then Ax)
(x)(IF Cx then NOT-Bx)

Darii

All A are B
Some C are A
Some C are B

(x)(IF Ax then Bx)
(Ex)(Cx AND Ax)
(Ex)(Cx AND Bx)

Ferio

No A are B
Some C are A
Some C are not B

(x)(IF Ax then NOT-Bx)
(Ex)(Cx AND Ax)
(Ex)(Cx AND NOT-Bx)

There are rules of inference. If you have a universal quantifier like (x) you can infer that any variable such as "a" has the same attributes.

So from

(IF Ax Then Bx)

we can infer IF Ay then By - if y has property A then y has property B.

from (IF Cx then Ax)

we can infer IF Cy then Ay

Since Ay, By, and Cy are propositions, we can construct a truth table for

(IF A then B) AND (IF C THEN A) implies (IF C THEN B)

and infer

IF Cy THEN By

Or, you can build a conditional proof by

1. Cy - assumption
2. IF Cy then Ay - assumption
3. Ay - 1,2,Modus Ponens
4. IF Ay then By - assumption
5. By - 3,4,Modus Ponens
6. IF Cy then By - 1,5,Conditional Proof

and by a rule known as Universal Instantiation we have

(x)(IF Cx THEN Bx)

More coming
 
Can Aristotelian logic deal with asymmetrical relations?

MASS = ENERGY
Mass is made up of energy, photons are made up of energy, photons are made up of mass.

Photons can only travel at light speed, because they have no mass, so I am wondering about, if Aristotelian logic can deal with asymmetrical relations? :D
 
If I understand your question, the answer is "no". An assymetrical relation (something like X is the father of Y) cannot be represented within the traditional syllogism.

X is the father of Y
Y is the father of Z
X is the grandfather of Z

requires other methods for evaluation.

Even symmetrical relations ("X is married to Y" implies "Y is married to X") don't work out.

Same for non-symmetrical relations (X loves Y)

(the above paraphrasing Kahane, page 160-161)

For such relations, predicate logic is required.

(I don't want to talk about mass/energy. The scientists here are much better qualified)
 

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