Note that Proposition 1' marks a shift from talk of cognition to
talk of consciousness. `Consciousness' is a narrower term
than `cognition.' Cognition, that is, includes consciousness.
It follows that if consciousness
isn't reversible,
then the broader phenomenon of cognition isn't either. (Of course,
many elements of cognition are computable.)
It's important to realize that we have something rather specific in mind when we use the term `consciousness' in this paper: we have in mind what is sometimes called phenomenal consciousness. Ned Block [8], in a recent essay on consciousness in Behavioral and Brain Sciences, calls this brand of consciousness P-consciousness. Here's part of his explication of this concept:
So how should we point to P-consciousness? Well, one way is via rough synonyms. As I said, P-consciousness is experience. P-conscious properties are experiential properties. P-conscious states are experiential states, that is, a state is P-conscious if it has experiential properties. The totality of the experiential properties of a state are ``what it is like" to have it. Moving from synonyms to examples, we have P-conscious states when we see, hear, smell, taste and have pains. P-conscious properties include the experiential properties of sensations, feelings and perceptions, but I would also include thoughts, wants and emotions. ([8], p. 230)
Block distinguishes between P-consciousness and A-consciousness; the latter concept is characterized as follows:
A state is access-conscious (A-conscious) if, in virtue of one's having the state, a representation of its content is (1) inferentially promiscuous, i.e., poised to be used as a premise in reasoning, and (2) poised for [rational] control of action and (3) poised for rational control of speech. ([8], p. 231)
Note that it's plausible to regard certain computational artifacts to be bearers of A-consciousness (e.g., theorem provers with natural language generation capability), whereas we shall now attempt to establish that P-consciousness (hereafter referred to by simply `consciousness') is beyond computation:
