RE: OK Christians. your chance. Convince me of God.
September 21, 2012 at 2:31 pm
(This post was last modified: September 21, 2012 at 2:38 pm by Mystic.)
No you can't think of that way, you have to work with what logicians means.
A ->B
A
Therefore B
Means A is sufficient for B being true.
While if B is true, it doesn't mean A is true.
A -> B
Not B
Therefore Not A
Means B is necessary for A to be true.
While if A is not true, it doesn't mean B is not true.
A->B
You have both a necessary condition (B) and sufficient condition (A).
If you do if only if,
Then you have A <->B
Which translates to
A->B
B->A
Then A is both sufficient and necessary condition for B, and B is both a sufficient and necessary condition for A.
This is called double implication.
Here is the verse from Quran:
أَفَلَا يَتَدَبَّرُونَ الْقُرْآنَ ۚ وَلَوْ كَانَ مِنْ عِنْدِ غَيْرِ اللَّهِ لَوَجَدُوا فِيهِ اخْتِلَافًا كَثِيرًا {82}
[Shakir 4:82] Do they not then meditate on the Quran? And if it were from any other than Allah, they would have found in it many a discrepancy.
A ->B
A
Therefore B
Means A is sufficient for B being true.
While if B is true, it doesn't mean A is true.
A -> B
Not B
Therefore Not A
Means B is necessary for A to be true.
While if A is not true, it doesn't mean B is not true.
A->B
You have both a necessary condition (B) and sufficient condition (A).
If you do if only if,
Then you have A <->B
Which translates to
A->B
B->A
Then A is both sufficient and necessary condition for B, and B is both a sufficient and necessary condition for A.
This is called double implication.
Here is the verse from Quran:
أَفَلَا يَتَدَبَّرُونَ الْقُرْآنَ ۚ وَلَوْ كَانَ مِنْ عِنْدِ غَيْرِ اللَّهِ لَوَجَدُوا فِيهِ اخْتِلَافًا كَثِيرًا {82}
[Shakir 4:82] Do they not then meditate on the Quran? And if it were from any other than Allah, they would have found in it many a discrepancy.
