Our empirical grounds are very limited: We have only seen conscious systems as they exist on Earth. To draw, on these grounds, universal conclusions about how any conscious system must be structured would be a reckless leap, if our theories are really supposed to be driven by empirical tests on conscious animals, which could have come out either way. Who knows how those crucial theory-driving experiments would have come out on very differently constructed beings from Andromeda Galaxy?
A truly universal theory of consciousness seems more likely to succeed if it draws broadly from a range of hypothetical cases, abstracting away from empirical details of implementation on Earth. So we must sit in our armchairs. However, armchair reflection about the consciousness of hypothetical beings has two huge shortcomings:
- Experts in the field reach very different conclusions when asked to reflect on what sorts of hypothetical beings would be conscious (all the way from panpsychism to views that require highly sophisticated cognitive abilities).
- Our judgments about such cases must be grounded in some sort of prior knowledge, such as our experience of beings here on Earth and our developmentally and socially and evolutionarily favored beliefs. And there seems little reason to trust such judgments outside the run of normal cases, for example, about the consciousness or not of large group entities under various conditions.
If you are moved by these concerns, you might think that the appropriate response is to restrict our theory to consciousness as it appears on Earth. But even just thinking about consciousness on Earth drops us into a huge methodological dilemma. If we treat introspective reportability as something close to a necessary condition for consciousness, then we end up with a very sparse view of the distribution of consciousness on Earth. And maybe that's right! But it also seems reasonable to think that consciousness might be possible without introspective reportability, e.g., in dogs and babies. And then it becomes extremely unclear how we determine whether it is present without begging big theoretical questions. How could we possibly determine whether an ant is conscious without begging the question against people with very different views than our own?
Could we forget about non-human animals and babies and restrict our (increasingly less general) theory of consciousness just to adult humans? Even here, I incline toward pessimism, at least for the medium-term future.
One reason is this: I see no near-term way to resolve the question of whether consciousness abundantly outruns attention. I think I can imagine two very different possibilities here. One possibility is that I have constant tactile experience of my feet in my shoes, constant auditory experience of the hum of the refrigerator, etc., but when I'm not attending to such matters, that experience drops out of memory so quickly and is so lightly processed that it is unreportable. Another possibility is that I usually have no tactile experience whatsoever of my feet in my shoes or auditory experience of the hum of the fridge unless these things capture my attention for some reason. These possibilities seem substantively distinct, and it's easy to see how a proponent of one can create a methodological error theory to explain away the judgments of a proponent of the other.
Now maybe there's a way around these problems. Scientists have often found ingenious ways to embarrass earlier naysayers! But still, there's such a huge spread between the best neuroscientific approaches (e.g., Tononi and Dehaene) and such a huge spread between the best philosophical approaches (e.g., Chalmers and Dennett), that it's hard for me to envision a well-justified consensus emerging in my philosophical lifetime.