The explanation of our reliability is not physical

1. All facts completely reducible to physics are first-order facts.

2. All facts completely explained by first-order facts are themselves completely reducible to first-order facts.

3. Facts about our epistemic reliability are facts about truth.

4. Facts about truth are not completely reducible to first-order facts.

5. Therefore, no complete explanation of our epistemic reliability is completely reducible to physics.

This is a variant on Plantinga’s evolutionary argument against naturalism.

Premise (4) follows from Tarski’s Indefinability of Truth Theorem.

The one premise in the argument that I am not confident of (2). But it sounds right.

Determinism and thought

Occasionally, people have thought that one can refute determinism as follows:

1. If determinism is true, then all our thinking is determined.

2. If our thinking is determined, then it is irrational to trust its conclusions.

3. It is not irrational to trust the conclusions of our thinking.

4. So, determinism is not true.

But now notice that, plausibly, even if we have indeterministic free will, other animals don’t. And yet it seems at least as reasonable to trust a dog’s epistemic judgment—say, as to the presence of an intruder—as a human’s. Nor would learning that a dog’s thinking is determined or not determined make any difference to our trust in its reliability.

One might respond that things are different in a first-person case. But I don’t see why.

Functionalism and imperfect reliability

Suppose a naturalistic computational theory of mind is true: To have mental states of a given kind is to engage in a particular kind of computation. Now imagine a conscious computer thinking various thoughts and arranged around standard logic gates. Modify the computer to have an adjustment knob on each of its logic gates. The adjustment knob can be set to any number between 0 and 1, such that if the knob is set to set to p, then the chance (say, over a clock cycle) that the gate produces the right output is p. Thus, with the knob at 1, the gate always produces the right output, with the knob at 0, it produces the opposite output, with the knob at 0.5, it functions like a fair coin. Make all the randomness independent.

Now, let C_p be the resulting computer with all of its adjustment knobs set to p. On our computational theory of mind, C₁ is a conscious computer thinking various thoughts. Now, C_0.5 is not computing anything: it is simply giving random outputs. This is true even if in fact, by an extremely unlikely chance, these outputs always match the ones that C₁ gives. The reason for this is that we cannot really characterize the components of C_0.5 as the logic gates that they would need to be for C_0.5 to be computing the same functions as C₁. Something that has a probability 0.5 of producing a 1 and a probability 0.5 of producing a 0, regardless of inputs, is no more an and-gate than it is a nand-gate, say.

So, on a computational theory of mind, C_0.5 is mindless. It’s not computing. Now imagine a sequence of conscious computers C_p as p ranges from 0.5 to 1. Suppose that it so happens that the corresponding “logic gates” of all of them always happen to give the same answer as the logic gates of C₁. Now, for p sufficiently close to 1, any plausible computational theory of mind will have to say that C_p is thinking just as C₁ is. Granted, C_p’s gates are less reliable than C₁’s, but imperfect reliability cannot destroy thought: if it did, nothing physical in a quantum universe would think, and the naturalistic computational theorist of mind surely won’t want to accept that conclusion.

So, for p close to 1, we have thought. For p = 0.5, we do not. It seems very plausible that if p is very close to 0.5, we still have no thought. So, somewhere strictly between p = 0.5 and p = 1, a transition is made from no-thought to thought. It seems implausible to think that there is such a transition, and that is a count against computational theories of mind.

Moreover, because all the gates actually happen to fire in the same way in all the computers in the C_p sequence, and consciousness is, on the computational theory, a function of the content of the computation, it is plausible that for all the values of p < 1 for which C_p has conscious states, C_p has the same conscious states as C₁. Either C_p does not count as computing anything interesting enough for consciousness or it counts as imperfectly reliably computing the same thing as C₁ is. Thus, the transition from C_0.5 to C₁ is not like gradually waking up from unconsciousness. For when we gradually wake up from unconsciousness, we have an apparently continuous sequence of more and more intense conscious states. But the intensity of a conscious state is to be accounted for computationally on a computational theory of mind: the intensity is a central aspect of the qualia. Thus, the intensity has to be a function of what is being computed. And if there is only one relevant thing computed by all the C_p that are computing something conscious-making, then what we have as p goes from 0.5 to 1 is a sudden jump from zero intensity to full intensity. This seems implausible.