I've been trying for over a year now to get a handle on Maydole's MPA, with limited success. I have only a limited knowledge of logic, and I'm trying to tame this thing down into a manageable, readable argument that any layman could understand without having to know all the background logic (other than, perhaps, a basic understanding of modus tollens/ponens). Even emails with Maydole and Oppy themselves didn't help much. I think once you become an academic it becomes difficult to dumb yourself down anymore.
This is what I have so far, which is only the first half (the possibility premise). Does this work as a basic capture of the core intuition?
1. If "maximal greatness" is not possible, then all properties entail "non-maximal-greatness"
2. The property of "Maximal greatness" cannot entail the property of "non-maximal greatness"
3. Therefore, "maximal greatness" is possible Premise 1 a tautology. Premise 2 is true because a great-making property cannot entail a lesser-making property, by definition. If a great-making property entailed a lesser-making property, then it would not be a great-making property in the first place. For example, if a plausibly great-making property such as "intelligence" also entailed the property of "being stuck in a hospital bed hooked up to wires", then "intelligence" would not in fact be a great-making property after all. Since "maximal greatness" is a great-making property, then it cannot entail a lesser-making property like "non-maximal-greatness."