Perhaps John fails to eat because his hands are temporarily paralyzed,
because he has been influenced by a hypnotic suggestion, or whatever.
This problem undercuts the claim that behavioral analyses of mental
states are elegant and insightful, suggesting instead that they are fatally
flawed or at least on the wrong track.
2.Inability to eliminate mental entities. The other problem is that the con-
ditionals that must be enumerated frequently make reference to just the
sorts of mental events that are supposed to be avoided. For example,
whether Johnseesthe food or not, whether heintendsto fast, and what he
believesabout its being poisoned are all mentalistic concepts that have now
been introduced into the supposedly behavioral definition. The amended
version is therefore unacceptable to a strict theoretical behaviorist.
For such reasons, theoretical behaviorism ultimately failed. The problem, in a
nutshell, was that behaviorists mistoo ktheepistemic statusof mental states
(how we come to know about mental states in other people) for theontological
statusof mental states (what their inherent nature is) (Searle, 1992). That is, we
surely come to know about other people’s mental states through their behavior,
but this does not mean that the nature of these mental states is inherently
behavioral.
Functionalism Functionalismwas a movement in the philosophy of mind that
began in the 1960s in close association with the earliest stirrings of cognitive
science (e.g., Putnam, 1960). Its main idea is that a given mental state can be
defined in terms of the causal relations that exist among that mental state,
environmental conditions (inputs), organismic behaviors (outputs), and other
mental states. Note that this is very much like behaviorism, but with the im-
portant addition of allowing other mental states into the picture. This addition
enables a functionalist definition of hunger, for example, to refer to a variety
of other mental states, such as perceptions, intentions, and beliefs, as sug-
gested above. Functionalists are not trying to explain away mental phenomena
as actually being propensities to behave in certain ways, as behaviorists did.
Rather, they are trying to define mental states in terms of their relations to
other mental states as well as to input stimuli and output behaviors. The picture
that emerges is very much like information processing analyses. This is not
surprising because functionalism is the philosophical foundation of modern
computational theories of mind.
Functionalists aspired to more than just the overthrow of theoretical behav-
iorism, however. They also attempted to bloc kreductive materialism by sug-
gesting new criticisms of mind-brain identity theory. The basis of this criticism
lies in the notion ofmultiple realizability: the fact that many different physical
devices can serve the same function, provided they causally connect inputs and
outputs in the same way via internal states (Putnam, 1967). For example, there
are many different ways of building a thermostat. They all have the same
function—to control the temperature in the thermostat’s environment—but
they realize it through very different physical implementations.
Multiple realizability poses the following challenge to identity theory. Sup-
pose there were creatures from some other galaxy whose biology was based
on silicon molecules rather than on carbon molecules, as ours is. Let us also
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