A tweak to the ontomystical argument

In an old paper, I argued that we do not hallucinate impossibilia: if we perceive something, the thing we perceive is possible, even if it is not actual. Consequently, if anyone has a perception—veridical or not—of a perfect being, a perfect being is possible. And mystics have such experiences. But as we know from the literature on ontological arguments, if a perfect being is possible, then a perfect being exists (this conditional goes back at least to Mersenne). So, a perfect being exists.

I now think the argument would have been better formulated in terms of what two-dimensional semanticists like Chalmers call “conceivability”:

1. What is perceived (perhaps non-veridically) is conceivable.

2. A perfect being is perceived (perhaps non-veridically).

3. If a perfect being is conceivable, a perfect being is possible.

4. A perfect being is possible.

5. If a perfect being is possible, a perfect being exists.

6. So, a perfect being exists.

Premise (3) follows from the fact that the notion of a perfect being is not twinearthable, so conceivability and possibility are equivalent for a perfect being (Chalmers is explicit that this is the case for God, but he concludes that God is inconceivable). Premise (1) avoids what I think is the most powerful of Ryan Byerly’s four apparent counterexamples to my original argument: the objection that one might have perceptions that are incompatible with necessary truths about natural kinds (e.g., a perception that a water molecule has three hydrogen atoms).

Is a necessary being inconceivable?

Consider this argument:

1. Obviously necessarily, if N is a necessary being that exists, it is impossible that N doesn't exist.
2. It is conceivable that N doesn't exist.
3. So it is inconceivable that N exists.

For this argument to work, we need to be able to make the inference from:

4. Obviously necessarily, if p, then necessarily q.
5. Conceivably not q.
6. So, not conceivably p.

Suppose that p just is the statement that necessarily q. Then (4) is uncontroversial. If the above argument form is good, then so is this one:

7. Conceivably not q.
8. So, not conceivably necessarily q.

But why can't we conceive both of not q and of necessarily q? Why should the ability to conceive of one thing, viz., the necessity of q, preclude the ability to conceive of another, viz., not q?

The principle that conceivability is defeasible evidence of possibility may seem relevant, but I don't think it establishes the point. That I can conceive of necessarily q is evidence of the necessity of q. That I can conceive of not q is evidence if the possibility of not q. So, if both, then I have evidence for two contradictory statements. Nothing particularly surprising there: quite a common phenomenon, in fact!

Suppose A and B are contradictory statements. It may be that evidence for A is evidence against B. But is evidence for A evidence against there being evidence for B? If it is, it is very weak evidence. Likewise, even given the principle that conceivability is evidence for possibility, the argument from (7) to (8) is very weak, much weaker than the inferential strength of this principle.

To summarize: The strength of the inference from (1) and (2) to (3) in the original argument is about equal to the strength of evidence that the existence of evidence for A provides against the existence of evidence against A. But the existence of evidence of A provides very little evidence against the existence of evidence against A. So the original argument is a very weak one. It would be improved if the conclusion were weakened to the claim that it is impossible that N exists, and then I would focus my attack on (2).