Roland's Razor

In an online discussion group we stumbled on something that just seems like common sense but which none of us have come across anywhere else and which has come to be dubbed "Roland's Razor" by Paul.  I think he just liked the alliteration but thanks anyway.

If Proponent_a uses an argument to come to Conclusion_a and Proponent_b uses the same argument to come to Conclusion_b and Conclusion_a and Conclusion_b are incompatible or mutually exclusive the the argument itself is not able to be used to distinguish between Conclusions_a and Conclusion_b. It is not that the argument is invalid, it can be a perfectly valid argument, but if it can be used to come to mutually incompatible conclusions then the argument can't be used to distinguish between the conclusions.

By way of example, suppose that a party is trying to decide between god_a and god_b both of whom make the claim that they are the one and only god. So Proponant_a makes the argument that "She prayed for someone to be healed, and she was healed therefore god_a exists" while Proponant_b makes the argument that "She prayed for someone to be healed, and she was healed therefore god_b exists". For the party trying to decide between god_a and god_b the argument "She prayed for someone to be healed and she was healed" can't be used to decide between god_a and god_b.