Download The thesis at issue here is this: whether or not the Argument from

The thesis at issue here is this: whether or not the Argument from Irreversibility
presented by Bringsjord in his paper “Cognition is not Computation: The Argument From
Irreversibility” ([1]) is sound or unsound. I believe it to be unsound, based on a simple
logical argument:
1) If the Argument from Irreversibility is sound, then nothing based on
irreversible physical processes is computation
2) What computers do is based on irreversible physical processes
3) If the Argument from Irreversibility is sound, what computers do is not
computation (1, 2)
4) What computers do is computation
5) The Argument from Irreversibility is unsound. (3, 4)
This logic is clearly valid, so the argument rests on the truth of premises 1, 2, and 4.
Premise 4, I hope, is uncontroversial – if it were false, then computer scientists would
have a lot more to worry about than the veracity of Computationalism! I believe Premise
1 is obvious given the arguments in the paper [1], but it still warrants some recap and
explanation.
The Argument from Irreversibility hinges on the assertion that cognition,
including consciousness, is not reversible. Bringsjord follows two main paths in backing
up this assertion: the first, phenomenological one attempts to demonstrate that reversal of
consciousness is logically impossible because we cannot conceive of it, while the second
contends that the actual physical processes going on in the brain are not physically
reversible, due in large part to increasing entropy, and therefore whatever these processes
entail, such as consciousness according to the Computationalist view, is not reversible. It
is this latter view that is of relevance here (I am assuming the first to lead nowhere,
because even as Bringsjord has admitted, “We have no outright proof that Pconsciousness is irreversible in this strong modal sense” [1]). The latter view entails that
nothing based on irreversible physical processes is computation, by the same logic that
leads Bringsjord to conclude that consciousness cannot be computation if it’s based on
irreversible physical processes (since computation is reversible). If the soundness of the
Argument from Irreversibility requires this physics-based assertion to be true, which
seems to be the case given the bulk of the argument in [1], then Premise 1 above is
certainly sound.
Premise 2 is based on the fact that computers are constructed of silicon chips, and
operate by pushing electrons around inside their wiring – a process that is certainly
irreversible in the physical sense. Computer processors dissipate large amounts of heat,
for example, which signifies a lack of thermodynamic equilibrium, and therefore a
system that cannot be reversed in the sense that Bringsjord requires of it.
Bringsjord, however, would probably have a ready response to this, hinging
around Premise 2: That, yes, today’s computers are based on irreversible physical
processes, but the significant aspects of those computers, viz. the information flow within
them, is reversible, and is translated faithfully to the physical level. That Bringsjord
would respond this way is implied by passages such as this:
Two different and determinate levels may be addressed by Theorem 1
[reversibility of computation] (and the like): perhaps there is the purely
mathematical level of the theorem itself, and then perhaps also what might be
called the “logic gate level” of computer engineering…. Computer engineers have
on hand physical instantiations of Turing Machines…. [B]oth theoretical
computers science and computer engineering is [sic] constrained and informed by
Theorem 1 and its relatives. [1, in footnotes]
This “logic gate level” seems to be the level of abstraction at which reversibility, and
computation, still hold, and that which is faithfully reproduced (that is, none of the
relevant behavior is lost) by the physical (yet nonreversible) instantiation.
I agree with this; however, there is a similar “way out” for consciousness and the
mind: perhaps there is a layer above the physical representation of the mind which
faithfully reproduces all relevant aspects (even p-consciousness) of the physical
instantiation, and which is reversible and therefore computable. Dennett [2] (quoted by
Bringsjord in [1]) seems to imply such a view:
The central doctrine of cognitive science is that there is a level of analysis, the
information-processing level, intermediate between the phenomenological level
(the personal level, or the level of consciousness) and the neurophysiological level
(p195).
Bringsjord also concisely represents this argument against him in [1] as: “‘…what you
fail to appreciate is that at the information-processing level to which Dennet has drawn
our attention consciousness is reversible…. you have surreptitiously moved at the same
time to a level beneath this level.’” And then, he provides his argument against this
whole concept -- representing the mind and consciousness -- and therefore the mind’s
“way out” of the problem of physical irreversibility:
The problem with this objection is that it conveniently ignores the fact that
computationalism is wed not only to information processing, but also to agent
materialism, the view that cognizers are physical things, and that therefore
cognition is a physical process. In light of this, introducing at least elementary
considerations from physics …[is] unavoidable. [1]
Bringsjord stresses this idea elsewhere (“…Computationalists as a rule hold that minds
are physical things” in a footnote in [1]). Therefore, it seems that Bringsjord is asserting
that using an abstract representation of the mind rather than regarding the actually
physical “stuff” is not Computationalism. However, I believe that this assertion is an
unfair characterization of Computationalism, and even a straw man attack.
The reason I believe it to be unfair is that an abstract representation of a physical
thing, which is very close to the physical thing in question, and that contains all the
relevant features of the physical thing, can be regarded as equivalent to that physical
thing for our discussion. In fact, Bringsjord uses exactly this idea when formulating his
characterization of Computationalism through Proposition 1’ (from [1]):
Proposition 1'. x(Px ^ x is conscious from ti to ti+k  y(My ^ x = y ^ Cj├y
Cj+1├y ├y Cj+p)), where this computation is identical to the consciousness x
enjoys through [ti, ti+k].
Notice the x = y, where x is a person and y is a Turing machine (or a neural network).
Persons (or their brains) are certainly physical things (assuming agent materialism), and
Turing machines are certainly abstract concepts. So in his own characterization of
Computationalism, Bringsjord is using the principle described above, where abstract
concepts and their accurate physical instantiations can be regarded as equal. In this case,
why can’t Computationalists deal with an accurate abstract representation of the physical
mind (for example, an insanely complex kind of neuron simulation network), which is
surely computation, and reversible, in the same way that computer engineers use the
“logic gate level” abstraction of the irreversible physical processes in the silicon of
computers? I can’t see any response except that “an accurate abstract representation of
the mind which involves all relevant physical aspects is impossible” – something for
which Bringsjord doesn’t make an argument in his paper. And it seems to me that if the
mind is purely physical, and is represented completely by our neurons and their
interactions, then a “neuron simulator” kind of neural-net approach (such physically
accurate simulators are in the works, such as CalTech’s GENESIS) would capture all
relevant aspects of the operation of the physical mind, and therefore would also capture
the mind’s consciousness. I see this notion fitting perfectly in Computationalism.
References:
[1] Bringsjord, Selmer. “Cognition is not Computation: The Argument From
Irreversibility.” Available from http://www.rpi.edu/~brings/pai.html.
[2] Dennett, D. (1993) ``Review of John Searle's The Rediscovery of the Mind," Journal
of Philosophy 90.4: 193-205