Wrt not implying substrate independence: sure, I agree in principle; it's not >impossible that only protoplasmic substrates can implement consciousness. All I'm saying is that if that turns out to be true, it will be because certain kinds of computations can only be performed on protoplasmic machines.

That is false, since we can build Universal Turing Machines (up to a certain finite memory) out of non-protoplasm, and a UTM can compute anything.

I suppose I could say my understanding of substrate-independence is implicitly a >2-place predicate: system S is subtrate-independent with respect to observer O iff O >considers some system S2 identical to S, where S is implemented on a different >substrate than S2.

An observer-relative notion of computation is problematic for a computational theory of consc, since an observer-relative notion of consciousness is problematics. Surely the point is that I know i am conscious, not that he thinks I am.