Putnam Brains in a Vat Well, what do you say wonderer1, is the BiV brain different than a real brain by having more parts or by having fewer parts?
wonderer1: I should rather think that a BiV brain cannot be compared to a real brain; they are completely different.
NotAristotle: As you say wonderer1, but then neither you nor I are a brain in a vat. We may be utterly deceived by our senses, but it is not by being a brain in a vat.
wonderer1: But I insist that we are brains in a vat; it must be so.
NotAristotle: Well then when we say brain we must mean something like a real brain.
wonderer1: Very well.
NotAristotle: Let us return then to our original inquiry: you seem to have said that a real brain is different than a BiV brain. But is it different by having more parts or fewer?
wonderer1: Surely it is by having fewer parts NotAristotle.
NotAristotle: Well put wonderer1, for if it had more parts, then it could be placed in a vat, just like a real brain. However, we are saying that it is impossible to place a BiV brain in a BiV vat. And this must be the case on account of a BiV brain having fewer parts than a real brain.
wonderer1: Indubitably.
NotAristotle: And what of our neuroscientists? Will they not be very much surprised to find that parts of our brains are missing?
wonderer1: Perhaps not.
NotAristotle: How do you mean wonderer1?
wonderer1: Perhaps the parts of the brain that are missing are not essential to perception, but are extra parts.
NotAristotle: Ah, I see, so these extra parts are excised, leaving behind the parts that are necessary for BiV perception.
wonderer1: Precisely.
NotAristotle: But if the parts that are necessary for perception are left intact, then once again, it should be possible to place a BiV brain in a BiV vat. But again, we have said this is impossible.
wonderer1: That is so.
NotAristotle: Then the problem arises once again, that our neuroscientists will likely find that parts of the brain are missing that are necessary for perception.
wonderer1: As you say NotAristotle.
NotAristotle: It stands to reason then, that if we are brains in a vat, the evidence will amount to saying that it should be impossible for us to perceive, given that we would be missing parts of the brain that are necessary for perception. In short, if we are brains in a vat, we will be missing parts of our brain, and neuroscientists will be quite perplexed by that.
wonderer1: Surely what you say is true NotAristotle.
NotAristotle: Well then wonderer1 that is good news. For, unless you and I are missing parts of our brains, we are most certainly not brains in a vat.
wonderer1: Good news indeed NotAristotle.