Ah, but as a brain-in-a-vat how could you distinguish other brains telling you things from the simulation just telling you what you want (or don't want) to hear

Ah, but as a brain-in-a-vat how could you distinguish other brains telling you things from the simulation just telling you what you want (or don't want) to hear? As long as we posit the "simulation" it doesn't really matter. EDIT: Pithyness. Solipsism is fun, isn't it? :) EDIT#2: I didn't mean to dismiss your point preemptively. I actually think it might be interesting to explore whether there could be (in principle) such a thing a shared-yet-simulated reality without succumbing to the solipsism argument. I don't think it's possible, but I'm not a philosopher. Incidentally physics has a similar problem. If you're interested, look up Boltzmann Brains and the "Arrow of Time".