FrankTrollman at [unixtime wrote:1078439385[/unixtime]]Your construct was based "logically" on using Contraposition on sets of directives - which is painfully invalid. Consider, Contraposition gives us things such as:
If you roll a 20 on your attack roll, you hit your opponent. Therefore: If you miss your opponent, you did not roll a 20 on your attack roll.
It just doesn't work. The fact that this thread has featured various so-called philosophy majors saying that it did, simply proves that the power of ignorance is all pervasive or something.
Er, Frank, that statement is true. If I missed my opponent, then I didn't roll a 20, did I? The statement "If you roll a 20 on your attack roll, you hit your opponent." is true if you roll a 19. Similarly, "If you miss your opponent, you did not roll a 20 on your attack roll." is also true. Because if I had rolled a 20, I would have hit.
"But I can roll a 19 and hit!"
So what? Neither premise deals with the instance of rolling a 19. The premise is predicated on rolling a 20. Those premises are not in any way saying "If you do not roll a 20 on your attack roll, you cannot hit your opponent." That would be the fallacy of leaping to conclusions. Or hasty generalization. One of the two.
Contrapositive is:
P -> Q becomes ~Q -> ~P
Not:
P -> Q becomes ~P -> ~Q
The former two statements are logically equivalent. Thet latter two are not.
Code: Select all
[br]Contrapositive Truth Table[br]--------------------------[br]P Q P->Q ~Q->~P ~P->~Q[br]T T T T T[br]T F F F T[br]F F T T T[br]F T T T F[br]
Column 4 is the contrapositive of 3. Column 5 is the negation of each side of the condititional in 3.
In order for the statement "If you roll a 20 on your attack roll, you hit your opponent." to be false, you must "roll a 20" AND "not hit". In order fot the stament "If you miss your opponent, you did not roll a 20 on your attack roll." to be false, you must "not hit" AND "roll a 20".
If you want to handle the case of rolling a 19, then P becomes false and both statements are always true.
The point is that logic doesn't prove exclusivity. The "truth" of a logical premise is constrained by the system it pertains to.
Edit: Added clarifications.