I was randomly reading Warranted Christian Belief (Plantinga) and came across his discussion of models in Chapter 6. The context was his presentation of the Aquinas/Calvin and the extended Aquinas/Calvin model. Cool and all, but not what caught my attention. There's, of course, Model Theory. But Plantinga proposes a use of the term 'model' that's more concrete than that. It won't have to do with how the natural numbers are a model for some 'consistent first-order theory'. Plantinga says that the 'model' will be a proposition. It can also be a state of affairs. It'll be a possible proposition, sure. And then Plantinga gives us a condition: if that possible proposition happens to be true, then so is what Plantinga calls 'the target proposition'. In this case, that proposition is, respectively, either theism is true or Christian theism is true. So, we have a pair of conditionals. Namely, if something like the proposed models are true, then so are the pair of target propositions. And both of the conditionals are true because the consequents of both the conditions can't be false, per what's stipulated about the implications. The first thing Plantinga tries to do is more modest than demonstrating the models to be true. He wants to show they're epistemically possible. This modality is consistent with what we know. And what we know is 'what all (or most) of the participants in the discussion agree on'. It is stronger than broad logical possibility (I think Plantinga identifies this modality with metaphysical possibility, the possibility of being metaphysically instantiated). But what's interesting is that a proposition can be epistemically possible, but not metaphysically possible. As an example, Plantinga considers existentialism: the existence of propositions ontologically depend on the existence of the singular objects of which they are about. In other words, the existence of the proposition Socrates is Greek ontologically depend on the existence of Socrates. Plantinga explains that he believes, but doesn't know, that existentialism is false. The belief in the falsity of existentialism is consistent with what we know. It is therefore epistemically possible. But curiously, belief in the truth of existentialism is also consistent with what we know. Thus, the proposition, along with its denial, is both epistemically possible, even though only one or the other is necessarily true, which means that one or the other is necessarily false. Therefore, a proposition can be epistemically possible, but metaphysically impossible.
That's all for now. I just thought it was interesting, perhaps another way to get at modal knowledge. Off to bed!
