"nothing but causal relationships" is indeed all you'd need, provided they go the materialist way, i.e. that consciousness comes from specific arrangements of neurons. I don't think that makes sense, as nobody can give the slightest hint of a theory that would make that work. The reverse theory, that consciousness is primary, makes more sense to me. In that theory, the causality works the other way, and digital replicas will not have consciousness, they will be a mirror of what consciousness looks like when seen through our senses.

>In that theory, the causality works the other way, and digital replicas will not have consciousness

Why not? Digital stuff is made up of matter as well. Unless there's something special about neurons when it comes to consciousness, i.e. the conscious bits reside in neurons and nowhere else for some reason, there's reason to think non-biological structures that produce the same output would also be conscious. Any substantive theory of consciousness, materialist or not, will need to include a place for structure and dynamics, i.e. information cascades, within their theory to account for the correlations we observe between conscious states and brain structure and dynamics. But these qualities are present in a digital implementation as well.

> I don't think that makes sense, as nobody can give the slightest hint of a theory that would make that work

I'm not sure what could possibly answer this problem, at least to the satisfaction of the people who think it is a problem. Personally, I'm relatively happy that Daniel Dennett's ideas demonstrate how what we think of as consciousness, qualia etc can be explained via mechanistic/algorithmic processes.

> and digital replicas will not have consciousness

They will also go on internet forums arguing that while they, of course, do have consciousness - the digital replicas of themselves would not!