There are four kinds of modal arguments that I shall consider in this section. The first kind turns on the use that can be made of the ‘actually’ operator; the second kind turns on the use that can be made of the ‘necessity’ operator; the third kind turns on a weak version of the principle of sufficient reason; and the fourth kind turns on the properties of incomprehensible beings.

MODAL ARGUMENTS INVOLVING ACTUALITY

A simple version of a modal ontological argument that involves the ‘actually’ operator is the following:

1. It is possible that it actually is the case that God exists. (Premise)

2. (Hence) God exists. (From 1)

There are modal logics in which this is a valid argument. In particular, if a “nonshifty” actually operator - that is, an actually operator that is such that even when it is embedded in the scope of other operators, it always refers back to the world of its utterance - is added to the modal logic S5, then the argument is valid.

However, if the actually operator is given a nonshifty reading, then there is no reason for an agnostic to assent to the premise. After all, on this reading, the possibility judgment in question just amounts to a judgment that God exists. Any reasonable agnostic will see equal merit in the following argument:

1. It is possible that it is actually the case that God does not exist. (Premise)

2. (Hence) God does not exist. (From 1)