Moe asks:

What do you think of Putnam’s argument against being a brain in a vat?

Assume we are brains in a vat.

If we are brains in a vat, then ‘brain’ does not refer to brain, and ‘vat’ does not refer to vat.

If ‘brain in a vat’ does not refer to brains in a vat, then ‘we are brains in a vat’ is false.

Thus if we are brains in a vat, then the sentence ‘we are brains in a vat’ is false.

Answer by Craig Skinner

Putnam’s argument is invalid. As indeed the wording of your question shows.

The statement ‘I am a brain in a vat’ is false whether I am a normal human (not a BIV) or a BIV. But I still don’t thereby know which I am.

To clarify:

If I am a normal human, then saying ‘I am a brain in a vat’ is obviously false.

If I am a BIV, then, as you say, my utterance ‘brain’ doesn’t refer to a 3-pound porridgy lump, it refers to a pattern of electrical impulses generated by the computer linked to the envatted brain, let’s call it ‘brain*’. Similarly, ‘vat’ refers to another pattern, call it ‘vat*’. So, when I say ‘I am a brain in a vat’ I mean ‘I am a brain* in a vat*’, which is false because I am not a brain* in a vat*, I am a brain in a vat.

Putnam’s error is to conclude that because ‘I am a brain in a vat’ is false whatever, then I can’t be a brain in a vat. The correct conclusion is that either I am not a brain in a vat or I am not a brain* in a vat*. But I don’t know which false proposition I am expressing.

Incidentally, I doubt it matters to a brain whether it’s in a glass vat connected to a supercomputer or whether (like mine) it’s in a tight-fitting, pitch-dark, bony vat connected to the outside world.