Now, we do have a reason that supports the idea that an MGB’s existence does not violate any necessary truths, and that is the Modal Perfection Argument devised by Robert Maydole. Now, in order to understand this argument, you have to understand that when an entity or statement is impossible, everything entails its negation, including the statement itself. As an example to prove that it is possible to have something entail its negation, take the statement, “Every statement that cannot be demonstrated true by direct observation is false.” If this statement were true, it would entail that it was false, since the statement cannot be demonstrated true by direct observation. So, a version of the argument (
from this video) goes like this:
P1: If a property is a great-making property (a fancy word for a property which is better to have)
, its negation is a lesser-making property (a fancy word for a property which is worse to have)
P2: Great-making properties do not entail lesser-making properties. (if one did, it wouldn’t be a great-making property after all)
P3: Maximal greatness is the greatest great-making property.
C1: Therefore, maximal greatness cannot entail its negation of non-maximal greatness
C2: Therefore, maximal greatness is possible.
Here is my issue with this line of thinking: The negation of an impossible proposition is entailed by every other proposition. This stems from the fact that a conditional whose consequent is true is always true.
But I do not see how we can use this fact in a non-circular way. Suppose I give you a proposition p. As long as “p” is not impossible, it will be the case that “L~(p ->~p),” that necessarily, p does not entail not p. But in order to make use of that fact, we have already assumed that p is possible.
The argument does “try to get around this” using P2 and P3. It attempts to show rather than assume that if you take maximal greatness to be a great-making property, then it will not entail its lesser-making property.
But I don’t think this will work non-circularly. Let’s make another parallel argument:
P1: If a property is a great-making property, its negation is a lesser-making property.
P2: If and only if a proposition p is possible, it will not entail its negation.
P3: Great-making properties do not entail lesser-making properties.
P4: p is a great-making property. (Assumption)
C1: ~p is a lesser-making property.
C2: p does not entail ~p.
C3: p is possible.
C4: All great-making properties are possible.
The problem with this argument is that it works for everything that we call a great-making property. By saying that something is a great-making property, we implicitly assume that it is possible. So the modal perfection argument does not seem to get above declaring that maximal greatness is possible. The circularity of the modal perfection argument implies that P2 in your shorter formulation gets support just from the lack of atheistic arguments for God’s impossibility:
P2 is supported by the Modal Perfection Argument, as well as the lack of any atheistic arguments for His impossibility that hold up to scrutiny.
So it does, as I said, rely on the premise that consistent conceivability implies real possibility.
Here is a potential atheistic objection that I find this argument vulnerable to: If maximal greatness implies immateriality, and an atheist is a physicalist, then he will find maximal greatness to be impossible.
On the contrary, Aquinas’s First Way, for instance, claims that the motion in the physical world requires that there exists some immaterial entity sustaining it. If one wants to get to immateriality from this modal argument, however, it is not clear how one does so, especially if the argument is presented to those with physicalist sympathies. I think a good argument should give a physicalist good reasons to abandon physicalism. But this argument does not, so it seems like the physicalist will not find reason to accept P2.