John Greco, How to Reid Moore:
So how does one know that one is not a brain in a vat, or that one is not deceived by an evil demon? Moore and Reid are for the most part silent on this issue. But a natural extension of their view is that one knows it by perceiving it. In other words, I know that I am not a brain in a vat because I can see that I am not. [. . .] Just as I can perceive that some animal is not a dog, one might think, I can perceive that I am not a brain in a vat. (21)
Really?
A bobcat just walked past my study window. I see that the critter is a bobcat, and seeing that it is a bobcat, I see that it is not a dog, or a deer or a javelina. So far, so good. But then John Greco comes along and tells me that in the same sense of 'see' — the ordinary visual-perceptual sense — I can see that I am not a brain-in-a-vat, a BIV. But 'surely' one cannot see or otherwise perceive such a fact. Or so I will argue.
Q1: How do you know you are not a BIV?
A1: I see that I am not.Q2: How do you know that you are not a creature of God?
A2: I see that I am not.
These question-answer pairs seem on a par. If the atheist says that he sees that he is not a creature of God, or more generally, sees that the manifest world is not a divine artifact, then we point out to him that this is not the sort of state of affairs that can either be seen to be the case or seen not to be the case. For no matter how intently one observes (whether visually or in any other sense-modality) anything in the natural world, one will not be able to discern whether or not it has creature-status. (By 'creature-status' I mean the ontological status of being a product of divine creative activity.) This is true of the objects of outer perception as well as the objects of inner peception, e.g. memories, desires, sensations, etc. And of course nothing is changed by the use of instruments. If I study the moon through a telescope, I will be in no better position to determine that it is a divine artifact than if I view it with the naked eye. Landing on the moon, taking geological selenological samples, won't help either. And the same goes for any instrumental extension of the human senses.
In sum, using 'see' to cover inner and outer sense-perception, whether 'naked' or instrumentally extended, one cannot see whether or not our world is a divine artifact. The same is true with respect to our BIV-status: one cannot see whether or not one is a BIV. For what would one look at, or look for, in order to make this out? Would I stare at the bobcat outside my window and try to isolate a property of the critter that would entail that its appearance to me is solely the result of the machinations of an evil scientist? Or would I look for a property that would entail the animal's not being such a result?
Or is there perhaps some particular thing I must search for the finding or nonfinding of which would resolve the question of whether I am a BIV? You may recall Soviet cosmonaut Yuri Gagarin's suborbital flight in April, 1961. He beat astronaut Alan Shepard to the punch by a couple of months. What remains with me from the news reports is Gagarin's claim to the effect that he didn't see God out there in outer space. I thought to myself at the time, "That dumb Commie thinks that God is a physical object floating around in outer space!" Later on it occurred to me that Gagarin might have made his statement just to please the Party ideologues back on the ground in Moscow. Now just as one cannot resolve the God question by poking around in outer space, one cannot resolve the BIV question by poking around in outer space or inner space.
The atheist who thinks that theism can be refuted by sense-perception is not understanding the issue. The same goes for the theist who thinks that theism can be proven by sense-perception. For the question does not concern observables, but the ontological status of observables. In Heideggerian jargon, it does not concern das Seiende, that-which-is, but das Sein, the Being of that-which-is. In particular, it concerns the ontological status, God-dependent existence.
Similarly, one who thinks that the problem of the external world, which is essentially the problem of the ontological status of the objects of outer perception, can be solved by perception, does not understand the issue. One cannot see that one is or is not a BIV, or dreaming, or being deceived by an evil demon, etc. The question is not about observables, but about their ontological status, their dependence on or independence of our minds.
I can see that the animal in front of me is a bobcat. So seeing, I see that the animal is not a dog. But no amount of observation can disclose that the object appearing to me either has or does not have the ontological status of mind-independent existence.
My point is connected with the one I made yesterday, namely, that one cannot refute an idealist such as Berkeley in some quick Moorean way by appealing to some obvious fact of sense-perception. The good bishop cannot be refuted by kicking a stone. For Berkeley is not denying that there are stones and such: he is forwarding a theory of their ontological status, and this status cannot be discerned by seeing or touching or experiencing resistance to kicking.