Consider the following: your consciousness, that experience you have of being, the one that --in the minds of many-- separates you from a computer programmed to behave like you, cannot exist under your model because it cannot be tested for. Consider also that this statement is ridiculous, because you clearly do have an experience of being. What does this tell us?
Empiricism and the scientific method are a philosophy for modelling reality, and they've undoubtedly done a bang up job of progressing human understanding, but that model is also incomplete. Think of it like Newtonian gravitation, another undoubtedly very useful model that, it turns out, is also incomplete.
I can generally agree that something like consciousness exists, because I seem to be experiencing it. The test of that fact is ongoing, as I type these words, and it continues to be true. I suspect, based on the fact that other people act like me and all also claim to be conscious, that they are having internal experiences similar to mine, although I can't know for sure.
So I don't agree that consciousness in general can't be tested for. We can test our own consciousness, and we can use induction to guess that at least other humans are experiencing something similar.
But you can't measure it objectively. You can't tell me that other people have consciousness, you just assume it is true because they seem to be like you. You have no mechanism for determining the limits of your assumption and indeed past societies have drawn the line in even narrower constraints than "human".
> you just assume it is true because they seem to be like you
A minor, but important point. I don't assume it's true. I just think it is more likely than not.
I suppose that the philosopher I'm talking about could say the same of their theory. And I guess that's OK, if all they're claiming is that this is something that seems likely. My only response to that would be that his induction is prima facie questionable to me.
Empiricism and the scientific method are a philosophy for modelling reality, and they've undoubtedly done a bang up job of progressing human understanding, but that model is also incomplete. Think of it like Newtonian gravitation, another undoubtedly very useful model that, it turns out, is also incomplete.