The Turing Test
Computing Machinery and
Intelligence
Alan Turing
Some Theories of Mind
• Dualism
– Substance Dualism: mind and body are differerent substances.
Mind is unextended and not subject to physical laws.
• Interactionism: mind and body interact
• Occasionalism/Parallelism: mind and body don’t interact
– Property/Event Dualism
• Epiphenomenalism: physical events cause mental events
but mental events don’t cause anything
• Property Dualism:(some) mental states are irreducibly nonphysical attributes of physical substances
Some Theories of Mind
• Physicalism: mental states are identical to physical states, in
particular, brain states or, minimally, supervene upon physical
states.
– (“Analytical” or “Logical”) Behaviorism: talk about mental
states should be analyzed as talk about behavior and behavioral
dispositions
– The Identity Theory (Type-Physicalism): mental states are
identical to (so nothing more than) brain states
– Functionalism: mental states are to be characterized in terms of
their causal relations to sensory inputs, behavioral outputs and
other mental states, that is, in terms of their functional role.
Dualism(s)
Pro
Con
• Qualia
• Causal closure of the physical
• Irreducibility of psychology
• Simplicity
• The Zombie Argument
• The Cartesian Essentialist
Argument
Descartes’ Arguments for Dualism
• Essentialist Argument
– It is conceivable that one’s mind might exist without one’s body
– Whatever is conceivable is logically possible
– Therefore, it is possible one’s mind might exist without one’s
body
• Empirical Argument
– The complexity and flexibility of human behavior, including
linguistic behavior, couldn’t be achieved by mere mechanism so
we need to assume some non-physical substance as an
explanation for such behavior.
The Zombie Argument
• A (philosophical) zombie is a being which is a perfect duplicate of a
normal human being—including brain and neural activity—but which
is not conscious.
• The Zombie Argument for property dualism
– Zombies are conceivable (David Chalmers singing the Zombie
Blues)
– Whatever is conceivable is logically possible
– (Some) mental states/properties/events are not identical to any
brain states/properties/events
• Note: this argument doesn’t purport to establish substance dualism
or, as Descartes wished to show, that minds/persons could exist in a
disembodied state.
Problem with Cartesian Dualism
• “We do not need that hypothesis”: complex behavior can be
explained without recourse to irreducibly non-physical states.
– Contra Descartes, purely physical mechanisms can exhibit the
kind of complex, flexible behavior, including learning (or
“learning”) characteristic of humans.
• All physical events have sufficient causes that are themselves
physical events
– Physicalism is an aggressor hypothesis: we explain more and
more without recourse to non-physical events/states
– Agency explanations are eliminated in favor of mechanistic
explanations—including explanations for agency itself.
– Claims to the effect that non-physical events cause physical
events introduces an even bigger mystery: what is the
mechanism?
Epiphenomenalism
• Motivation for Epiphenomenalism
– All physical events have sufficient causes that are themselves
physical events
– But some mental events—qualitative states, the what-it-is-like
experience—seem to be irreducibly nonphysical: it seems
implausible to identify them with brain events.
• Problem: intuitively some mental states cause behavior
– E. g. pain causes people to wince
– Moreover, part of what we mean by “pain” seems to involve an
association* of with characteristic behavior
*We’ll leave “association” intentionally vague
(Philosophical) Behaviorism
• Motivation
– We want to hold that there are no irreducibly non-physical
causes of physical events
– But we also need to accommodate the fact that what we mean
by terms designating mental states involves an association with
characteristic behavior.
• Problems
– Intuitively, there’s more to some mental states: the problem of
qualia
– Intuitively, there can be less to mental states: it’s conceivable
that one may be in a given state without even being disposed to
characteristic behavior—or that one may be disposed to
uncharacteristic behavior
– Dispositions aren’t causes so, while behaviorism associates
mental states with behavior, they still don’t cause behavior.
The Identity Theory
• Motivation
– We want to hold that there are no irreducibly non-physical
causes of physical events
– But we also want to understand them as “inner states” that are
causally responsible for behavior
• Problems
– Qualia again: intuitively there is more to consciousness than
brain states
– Species chauvinism: if we identify a type of mental state, e.g.
pain, with a type of brain state that is responsible for pain in
humans, e.g. the firing of C-fibers, what do we do about nonhumans who don’t have the same kind of brain states but who,
we believe, can never the less have the same kind of mental
states?
What a theory of mind should do
• Make sense of consciousness: “The Hard Problem”
• Avoid commitment to irreducibly non-physical states, events or
substances
• Explain the causal role of mental states as
– Effects of physical events
– Causes of behavior
– Causes of other mental events
• Allow for multiple realizability in order to avoid species
chauvinism
– We want to be able to ascribe the same kinds of mental states
we have to humans who may be wired differently, other animals
and, possibly to beings that don’t have brains at all, e.g.
Martians, computers
Functionalism
• What makes something a mental state of a particular type does not
depend on its internal constitution, but rather on the way it
functions, or the role it plays, in the system of which it is a part.
– Note: “function” here related also to “function” in math sense.
• Topic Neutrality: mental state concepts don’t specify their intrinsic
character, whether physical or non-physical—that’s a matter for
empirical investigation.
– So Functionalism is in principle compatible with both physicalism
and dualism
• Multiple Realizability: A single mental kind (property, state, event)
can be "realized" by many distinct physical kinds.
– The same type of mental state could, in principle, be “realized”
by different physical (or non-physical) states
– Disagreement about how “liberal” we should be in this regard
An Example: Pain
• We’re interested in analyzing or ordinary concept of pain
• We understand it in terms of its causal role
– As being typically produced by certain stimuli, e.g. bodily injury
– As tending to produce certain behavior, e.g. wincing
– As producing further mental states, e.g. resolving to avoid those
stimuli in the future
• We recognize that different kinds of physical (of non-physical)
mechanisms may play that role
– Compare to other functional concepts like “can opener”
– We leave empirical questions to empirical investigation
The Big Questions About Functionalism
• Consciousness: some mental states appear to have intrinsic,
introspectable features—and those features seem to be essential
– Inverted Qualia (see Block “Inverted Earth”)
– Zombies
– The Knowledge Argument (see Jackson “What Mary Didn’t
Know”)
• Understanding: controversial whether understanding can be
reduced to the ability to mediate input and output by manipulating
symbols (see Turing “Computing Machinery and Intelligence” vs.
Searle on The Chinese Room
The Turing Test
• Functionalism: mental states are to be characterized in terms of
their causal relations to sensory inputs, behavioral outputs and other
mental states, that is, in terms of their functional role.
• A Turing Machine can do this!
• So if Functionalism is true, a machine should in principle be able to
do anything a person can do
• Can a machine do whatever a person can do?
• And can it meet…
The Cartesian Challenge
If there were machines which bore a resemblance to our bodies and
imitated our actions as closely as possible for all practical purposes,
we should still have two very certain means of recognizing that they
were not real men. The first is that they could never use words, or
put together signs, as we do in order to declare our thoughts to
others. For we can certainly conceive of a machine so constructed
that it utters words, and even utters words that correspond to bodily
actions causing a change in its organs. … But it is not conceivable
that such a machine should produce different arrangements of
words so as to give an appropriately meaningful answer to whatever
is said in its presence, as the dullest of men can do. Secondly, even
though some machines might do some things as well as we do
them, or perhaps even better, they would inevitably fail in others,
which would reveal that they are acting not from understanding, but
only from the disposition of their organs. For whereas reason is a
universal instrument, which can be used in all kinds of situations,
these organs need some particular action; hence it is for all practical
purposes impossible for a machine to have enough different organs
to make it act in all the contingencies of life in the way in which our
What can people do that computers can’t do?
• Telling Humans and Computers Apart Automatically
• A CAPTCHA is a program that protects websites against bots by
generating and grading tests that humans can pass but current
computer programs cannot. For example, humans can read distorted
text as the one shown below, but current computer programs can't:
• The term CAPTCHA (for Completely Automated Public Turing Test To
Tell Computers and Humans Apart) was coined in 2000 by Luis von
Ahn, Manuel Blum, Nicholas Hopper and John Langford of Carnegie
Mellon University.
Empirical and Conceptual Questions
• The Turing Test: Can a machine* meet the Cartesian challenge?
– Use language in a way that humans do rather than merely
uttering sounds?
– Exhibit the complexity and flexibility of behavior in a wide range
of areas as humans do?
• What, if anything, of philosophic interest would it show if a machine
could pass the Turing Test?
– Is passing the test necessary for intelligence?
– Is passing the test sufficient?
* What is a “machine”? Aren’t our brains themselves machines?
Some Chatbots
• Eliza
• Alice
• Suzette
• Jack the Ripper
• POMO generator
• Poetry generator
• Chatbot
Collection
WFF
The Babbage Engine
ENIAC
Build your own Turing Machine!
A Turing machine is a theoretical computing machine invented by Alan Turing
(1937) to serve as an idealized model for mathematical calculation. A Turing
machine consists of a line of cells known as a "tape" that can be moved back
and forth, an active element known as the "head" that possesses a property
known as "state" and that can change the property known as "color" of the
active cell underneath it, and a set of instructions for how the head should
modify the active cell and move the tape (Wolfram 2002, pp. 78-81). At each
step, the machine may modify the color of the active cell, change the state of
the head, and then move the tape one unit to the left or right.
[read more in Wolfram MathWorld]
A Turing Machine is an Abstract Machine
An abstract machine is a model of a
computer system (considered either as
hardware or software) constructed to
allow a detailed and precise analysis
of how the computer system works.
Such a model usually consists of input,
output, and operations that can be
preformed (the operation set), and so
can be thought of as a processor. An
abstract machine implemented in
software is termed a virtual machine,
and one implemented in hardware is
called simply a "machine.”
[Wolfram Mathworld]
Turing Machine here: try it!
Another Turing Machine
A concrete Turing Machine
Different hardware – same abstract machine
We’re in the same
computational state!
• Mental states are like computational states of computers
• The same computational or mental state can be realized by different
hardware or brainware!
The Imitation Game
• Turing proposes a ‘game’ in which we have a person, a machine,
and an interrogator—separated from the other person and the
machine.
• The object of the game is for the interrogator to determine which of
the other two is the person, and which is the machine.
“I believe that in about fifty years’ time,” Turing wrote in 1950, “it
will be possible to programme computers…to make them play the
imitation game so will that an average interrogator will not have
more than 70% chan ce of making the right identification after five
minutes of questioning…I believe that at the end of the century the
use of words and general educated opinion will have altered so
much that one will be able to speak of machines thinking without
expecting to be contradicted.”
• So far this hasn’t happened but…there is a contest on:
The Empirical Question: Can a machine pass?
The Loebner Prize: In 1990 Hugh Loebner agreed with The
Cambridge Center for Behavioral Studies to underwrite a contest
designed to implement the Turing Test. Dr. Loebner pledged a
Grand Prize of $100,000 and a Gold Medal (solid—not gold-plated!)
for the first computer whose responses were indistinguishable from
a human's.
The Conceptual (Philosophical) Question
If the meaning of the words ‘machine’ and ‘think’ are to be found
by examining how they are commonly used it is difficult to escape
the conclusion that the meaning and the answer to the question,
‘Can machines think’ is to be sought in a statistical survey such as
a Gallup poll. But this is absurd. Instead of attempting such a
definition I shall replace the question by another, which is closely
related to it and is expressed in relatively unambiguous words.
• How is the question (of whether a machine could pass the Turing
Test) related to the question of whether a machine can think?
• What would it show if a machine could pass the Turing Test?
– Is being able to pass the Turing Test a necessary condition on
intelligence?
– Is being able to pass the Turing Test a sufficient condition on
intelligence?
Behaviorism?
The new problem has the advantage of drawing a fairly sharp line
between the physical and intellectual capacities of a man. No
engineer or chemist claims to be able to produce a material which is
indistinguishable from the human skin…but even supposing this
invention available we should feel there was little point in trying to
make a ‘thinking machine’ more human by dressing it up in such
artificial flesh.
• What matters for ‘intelligence’—or whatever Turing is testing for?
– Does ‘the right stuff’ (brain-stuff, ‘spiritual substance,” or
whatever) matter?
– Does the right internal structure or pattern of inner workings
matter? If so, at what level of abstraction?
– Does the right history, social role or interaction with environment
beyond interrogation and response in the Turing Test matter?
Objections Turing Considers
1.
The Theological Objection
2.
The ‘Heads in the Sand’ Objection
3.
The Mathematical Objection
4.
The Argument from Consciousness
5.
Arguments from Various Disabilities
6.
Lady Lovelace’s Objection
7.
Argument from Continuity in the
Nervous System
8.
Argument from the Informality of
Behavior
9.
Argument from Extrasensory
Perception
The Theological Objection
Thinking is a function of man’s immortal soul. God has given an
immortal soul to every mabn and women, but not to any other
animal or to machines. Hence no animal or machine can think.
• Turing’s response: God could give a machine a soul if he wanted to
• Some questions:
– Zombies. On this account it would be a contingent fact that
intelligent computers (or humans) had souls—soulless zombies
could perfectly simulate ensouled humans or machines.
– Are souls, if there are such things, what matter for
consciousness (vide Locke)
The ‘Heads in the Sand’ Objection
• The consequences of machines
thinking would be too dreadful. Let
us hope and believe that they
cannot do so.
• Turing notes that there’s no real
argument here.
• Nevertheless, the prospect of
intelligent machines raises a
number of ethical questions…
The Mathematical Objection
• Gödel’s theorem…shows that in any sufficiently powerful logical
system statements can be formulated which can neither be proved
nor disproved within the system.
• Consequently there will be some questions
a machine (being essentially an automated
formal system) cannot answer.
• Turing notes however that there are
questions that humans can’t answer
and it could be that beyond this we’re
bound by the same constraint that restricts
the capacity of machines.
The Argument from Consciousness
No mechanism could feel (and not merely artificially signal, an easy
contrivance) pleasure at its successes, grief when its valves fuse, be
warmed by flattery, be made miserable by its mistakes, be charmed
by sex, be angry or depressed when it cannot get what it wants.
• A machine that passed the Turing Test would, ipso facto, be able to
give appropriate responses to questions about poetry, emotions, etc.
• If we require more than the Turing Test as evidence of
consciousness then we have no good reason to believe that other
humans are conscious.
• But we do have good reason to believe that other humans are
conscious.
• Therefore the Turing Test would be evidence of consciousness in a
machine if that machine could pass the test.
Arguments from Various Disabilities
These arguments take the form, ‘I grant you that you can make
machines do all the things you have mentioned but you will never be
able to make one to…be kind, be resourceful, be beautiful, be
friendly, have initiative, have a sense of humor, tell right from wrong,
make mistakes, fall in love, enjoy strawberries and cream, make
someone fall in love with it, learn from experience, use words
properly, be the subject of its own thought, have as much diversity of
behavior as a man, do something really new.
• It seems likely that we can construct machines that will be able to do
a great many of these things—including learning and making
mistakes but
• We should also ask whether various items on the list are
requirements for intelligence or whether we’re building in a specieschauvinistic requirement that would exclude intelligent beings that
Lady Lovelace’s Objection
‘The Analytical Engine has no pretensions to originate anything. It
can do whatever we know how to order it to perform’
• But computers can surprise us and
• People aren’t all that original anyway
Final Objections
• Argument from Continuity of the Nervous System
– Response: a digital machine can imitate an analogue machine
• Argument from the Informality of Behaviour
– Response: no reason to think human behavior is any less rulegoverned
• Argument from Extrasensory Perception
– Taking ESP seriously, we could find ways to rule it out by putting
competitors in a ‘telepathy-proof room.’ Surely, even if ESP
were a reality it wouldn’t be any more of a requirement for
intelligence than the ability to appreciate strawberries and
cream.
• Learning
– In fact computers can, at least ‘learn’ and, unless we’ve
established independently that they aren’t intelligent, no reason
Imitation and Replication
• When is imitating X replication—i.e. another instance of X—rather
than mere simulation?
• When does the ‘right stuff’ matter:
– Margerine is only simulated butter but
– Walking with an artificial leg is real walking
• When do the right extrinsic features, e.g. right history matter:
– Counterfeit money and art forgeries are fakes but
– A copy of a file or application is the real thing
Are inputs/outputs all that matter?
Consider, for example, Ned Block's
Blockhead…a creature that looks just
like a human being, but that is controlled
by a “game-of-life look-up tree,” i.e. by
a tree that contains a programmed
response for every discriminable input at
each stage in the creature's life. If we
agree that Blockhead is logically
possible, and if we agree that Blockhead
is not intelligent (does not have a mind,
does not think), then Blockhead is a
counterexample to the claim that the
Turing Test provides a logically sufficient
condition for the ascription of
intelligence. After all, Blockhead could
be programmed with a look-up tree that
produces responses identical with the
ones that you would give over the entire
course of your life (given the same
Objections to the Turing Test as What Matters
• Intentionality (The Chinese Room: Searle, “Minds, Brains and
Programs”)
– You can’t crank semantics out of syntax: mere symbolmanipulation, however adept, doesn’t create meaning or
understanding.
• Consciousness (The Inverted Spectrum: Block, “Inverted Earth”)
– Neither behaviorism nor functionalism can capture the felt,
intrinsic character of phenomenal mental states, e.g. “what it is
like” to see red.
• Semantic Externalism (Swampman: Davidson, “Knowing One’s
Own Mind”)
– What one's words mean—if they mean—is determined not
merely by some internal state, but also by the causal history of
Intentionality Objection
What does “CKApqrr” mean? According to the syntactic rules of the
first game, “Shak-A-WFF,” it’s a WFF but when I construct and
manipulate WFFs I don’t know what I’m doing.
Consciousness: the Inverted Qualia Objection
[T]he inverted spectrum argument is this: when you and I have
experiences that have the intentional content looking red, your
qualitative content is the same as the qualitative content that I have
when my experience has the intentional content of looking green.
We use color words in the same way, make the same inferences,
and respond in the same way to the same stimuli but (it seems to be
conceivable that) our experiences are different in their intrinsic,
qualitative character: ‘what it is like’ to see red is different from
‘what it is like’ for me. The Turing Test can’t capture the ‘what it is
like’ feature of experience.
Semantic Externalism
Consciousness: The Zombie Problem
It seems conceivable that a being with NO qualia could pass the
Turning Test. Do qualia matter? If so, for what?