FRDB Archives

Freethought & Rationalism Archive

The archives are read only.


Go Back   FRDB Archives > Archives > IIDB ARCHIVE: 200X-2003, PD 2007 > IIDB Philosophical Forums (PRIOR TO JUN-2003)
Welcome, Peter Kirby.
You last visited: Today at 05:55 AM

 
 
Thread Tools Search this Thread
Old 04-11-2003, 02:39 AM   #31
Moderator - Science Discussions
 
Join Date: Feb 2001
Location: Providence, RI, USA
Posts: 9,908
Default

Another page on the conditional operator:

http://www.datanation.com/fallacies/distract/if.htm

Quote:
The proposition If P then Q is true if and only if either P is false or Q is true. It is false only when P is true and Q is false.
Thinking about this some more, my statement that the truth of "if P then Q" is independent of the truth-value of P was actually somewhat confused. For example, if Q is false, then "if P then Q" is true if P is true, but false if P is false, so in that sense it does depend on the truth-value of P. But that isn't quite what I was trying to get at. Now that I think about it, I actually need to use the some ideas from "modal logic" to express what I was trying to get at in formal terms. Modal logic deals with the question of whether a given statement is true in all possible worlds, false in all possible worlds, or true in some possible worlds but false in others. In these terms, what I meant was that for a statement of the form "if p then q", if it is true that in every possible world where p is true, q is also true, then "if p then q" is a necessary truth that is true in all possible worlds, even those where p happens to be false.

For example: "if I had two dinosaurs and I added one more, then I'd have three dinosaurs".

Now, in every possible world where I have two dinosaurs and I add one to it, it is true that I have three dinosaurs. Thus, this is a necessary truth, and it's true even in worlds like our own where I don't have any dinosaurs.

Similarly, consider "If God knows all true facts about the universe and there is a true fact about a particle's exact position and momentum, then God knows a particle's exact position and momentum". In all possible worlds where the if-statement is true, the then-statement would be true as well, therefore this is a necessary truth which is true in all possible worlds, even ones where it's false that God knows all true facts or that there is a true fact about a particle's exact position and momentum.

Here's a page talking the rules of modal logic:

http://plato.stanford.edu/entries/logic-modal/

The idea I am talking about is expressed formally in the section on possible worlds semantics:

Quote:
The truth value of the atomic sentence p at world w given by the valuation v may be written v(p, w). Given this notation, the truth values (T for true, F for false) of complex sentences of modal logic for a given valuation v (and member w of the set of worlds W) may be defined by the following truth clauses. (‘iff’ abbreviates ‘if and only if’.)

(~) v(~A, w)=T iff v(A, w)=F.

() v(AB, w)=T iff v(A, w)=F or v(B, w)=T.

(5) v(A, w)=T iff for every world w' in W, v(A, w')=T.
Here, is the conditional operator again, and A means "A is necessarily true (true in all possible worlds). Substituting () into (5), it is possible to show that:

v((AB), w)=T iff for every world w' in W, v(A, w')=F or v(B, w')=T.

This is the point I was making above. It takes a somewhat obscure area of logic to express it formally, but expressed in english I think it's clear enough. If B is true in every possible world where A is true, then "AB" is a necessary truth.
Jesse is offline  
Old 04-14-2003, 08:55 PM   #32
Seraphim
Guest
 
Posts: n/a
Default

Ok, I have an hour or so before going off outstation. I won't be around for a few days ... try not to miss me

Based on that site Jesse gave : P ---> Q

Conditional P ---> Q

If P, then Q = P implies Q
Irregulaties in Physics implies God doesn't know about it?

My reply - No, it says nothing about God.

Q follows from P = not P unless Q
Either concepts (theology or Religion) can support each other because one deals with Logics and Maths and another deals with beliefs.

My reply - Again NO, either implies one another.

Q if P = P only if Q
Irregulaties in Physics happens ONLY if God is directly responsible for it. He is or Is He not?

My reply - No again.

Whenever P, Q
Whenever one condition occurs, so does the other.
If irregulaties occurs, it means God knows about it.

My reply - This could be a proof of God by studying Irregulaties BUT so far, no one come forward and said he found God. So another NO.

P is sufficient for Q = Q is NECESSARY for P
Is Irregulaties in Physics necessary for God? Is God necessary for Irregulaties in Physics? So far from what I see, both concepts are has nothing to do with each other.

My reply - No again.

[/b]P is a sufficient condition for Q [/b]
Q is necessary for P. Is it so? Is Irregulaties in Physics necessary for anything related to God? Is concept of God necessary for anything related to Irregulaties in Physics.

My reply - No.

So far, all the conditional requirement for P ---> Q is above and it doesn't says anywhere that concept of God has anything to do with the Irregulaties in Physics.

Some Phrasings of Bionditional : P <---> Q

P if and ONLY If Q
Condition for P is acceptable ONLY IF condition to Q is acceptable.

IF and ONLY IF you guys believe in God than Irregulaties in Physics is an acceptable condition. Well? Do you? (Last I check, faith wasn't exactly a strong point among people here).

P is necessary and sufficient for Q

This condition ONE of the conditions which your claims could be legitimate. By stating that one condition is sufficient to support the other, you guys can claim that Irregulaties in Physics is sufficient to stating that God is a dork.

P is equivalent to Q

This is another condition where your claims is legitimate. By stating that Irregulaties in Physics is equivalent to Act of a Dork God, then this is logical.

So from all the conditions of P ---> Q above (all 9 of them), only 2 conditions supports that God has anything to do with Irregulaties in Physics (the last two).

PS : Sorry for the late reply, I was required outstation (and still does, about to leave) all the sudden. Thank You for the wait.
 
Old 04-14-2003, 09:11 PM   #33
Moderator - Science Discussions
 
Join Date: Feb 2001
Location: Providence, RI, USA
Posts: 9,908
Default

Seraphim, now I know you're not paying any attention to what I write. I have said over and over that my "if" condition--the "P"--is not "irregularities in physics". It is this:

P: God is "omniscient" (which I define to mean 'knows every true fact about reality') and there is a true fact about the simultaneous position and momentum of particles.

Q: God knows the simultaneous position and momentum of particles.

Now, you don't have to believe the statement P to recognize that "if P, then Q" is true. That's my point--an "if P then Q" statement does not depend on whether P actually is true, it just depends on whether Q would be true if P were true. For example:

P: Humans are reptiles, and all reptiles have feathers

Q: Humans have feathers.

Here, "if P then Q" is necessarily true since Q is a logical consequence of P, even though in our world P is clearly false.

So, do you disagree with the basic idea that the truth of an "if P, then Q" statement is totally independent of whether P is in fact true or false in reality? Please don't talk about God in your answer, I'm just asking a general question about statements of the form "if P, then Q".
Jesse is offline  
 

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Forum Jump


All times are GMT -8. The time now is 03:43 PM.

Top

This custom BB emulates vBulletin® Version 3.8.2
Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.