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The Little Thoughts of Thinking Machines

John McCarthy

Computer Science Department

Stanford University

Stanford, CA 94305



When we interact with computers and other machines, we often use lan-

guage ordinarily used for talking about people. We may say of a vending

machine, ‘It wants another ten cents for a lousy candy bar.’ We may say

of an automatic teller machine, ‘It thinks I don’t have enough money in my

account because it doesn’t yet know about the deposit I made this morning.’

This article is about when we’re right or almost right in saying these things,

and when it’s a good idea to think of machines that way.

For more than a century we have used machines in our daily lives whose

detailed functioning most of us don’t understand. Few of us know much

about how the electric light system or the telephone system work internally.

We do know their external behavior; we know that lights are turned on and

off by switches and how to dial telephone numbers. We may not know much

about the internal combustion engine, but we know that a car needs more

gas when the gauge reads near EMPTY.

In the next century we’ll be increasingly faced with much more complex

computer based systems.

It won’t be necessary for most people to know

very much about how they work internally, but what we will have to know

about them in order to use them is more complex than what we need to

know about electric lights and telephones. As our daily lives involve ever

more sophisticated computers, we will find that ascribing little thoughts to

machines will be increasingly useful in understanding how to get the most

good out of them.

Much that we’ll need to know concerns the information stored in comput-

ers, which is why we find ourselves using psychological words like ‘knows’,

‘thinks’, and ‘wants’ in referring to machines, even though machines are very

different from humans and these words arose from the human need to talk

about other humans.

According to some authorities, to use these words, the language of the

mind, to talk about machines is to commit the error of anthropomorphism.

Anthropomorphism is often an error, all right, but it is going to be increas-

ingly difficult to understand machines without using mental terms.

Ever since Descartes, philosophically minded people have wrestled with

the question of whether it is possible for machines to think. As we interact

more and more with computers — both personal computers and others — the

questions of whether machines can think and what kind of thoughts they can

have become ever more pertinent. We can ask whether machines remember,

believe, know, intend, like or dislike, want, understand, promise, owe, have

rights or duties, or deserve rewards or punishment. Is this an all-or-nothing

question, or can we say that some machines do some of these things and not

others, or that they do them to some extent?

My answer is based on work in the field of artificial intelligence (usually

abbreviated AI) which is the science and engineering of making computers

solve problems and behave in ways generally considered to be intelligent.

AI research usually involves programming a computer to use specific con-

cepts and to have specific mental qualities. Each step is difficult, and different

programs have different mental qualities. Some programs acquire informa-

tion from people or other programs and plan actions for people that involve

what other people do. Such programs must ascribe beliefs, knowledge and

goals to other programs and people. Thinking about when they should do

so led to the considerations of this article.

AI researchers now believe that much behavior can be understood using

the principle of rationality:

It will do what it thinks will achieve its goals.

What behavior is predicted then depends on what goals and beliefs are

ascribed. The goals themselves need not be justified as rational.

Adopting this principle of rationality, we see that different machines have

intellectual qualities to differing extents. Even some very simple machines

can be usefully regarded as having some intellectual qualities. Machines have

and will have varied little minds. Long before we can make machines with

human capability, we will have many machines that cannot be understood

except in mental terms. Machines can and will be given more and more in-

tellectual qualities; not even human intelligence is a limit. However, artificial

intelligence is a difficult branch of science and engineering, and, judging by

present slow progress, it might take a long time. From the time of Mendel’s

experiments with peas to the cracking of the DNA code for proteins, a hun-

dred years elapsed, and genetics isn’t done yet.

Present machines have almost no emotional qualities, and, in my opinion,

it would be a bad idea to give them any. We have enough trouble figuring

out our duties to our fellow humans and to animals without creating a bunch

of robots with qualities that would allow anyone to feel sorry for them or

would allow them to feel sorry for themselves.

Since I advocate some anthropomorphism, I’d better explain what I con-

sider good and bad anthropomorphism. Anthropomorphism is the ascription

of human characteristics to things not human. When is it a good idea to do

this? When it says something that cannot as conveniently be said some other


Don’t get me wrong. The kind of anthropomorphism where someone says,

‘This terminal hates me!’ and bashes it, is just as silly as ever. It is also

common to ascribe personalities to cars, boats, and other machinery. It is

hard to say whether anyone takes this seriously. Anyway, I’m not supporting

any of these things.

The reason for ascribing mental qualities and mental processes to ma-

chines is the same as for ascribing them to other people. It helps understand

what they will do, how our actions will affect them, how to compare them

with ourselves and how to design them.

Researchers in artificial intelligence (AI) are interested in the use of men-

tal terms to describe machines for two reasons. First we want to provide

machines with theories of knowledge and belief so they can reason about

what their users know, don’t know, and want. Second what the user knows

about the machine can often best be expressed using mental terms.

Suppose I’m using an automatic teller machine at my bank. I may make

statements about it like, ‘It won’t give me any cash because it knows there’s

no money in my account,’ or, ’It knows who I am because I gave it my secret

number’. We need not ascribe to the teller machine the thought, ‘There’s no

money in his account,’ as its reason to refuse to give me cash. But it was

designed to act as if it has that belief, and if I want to figure out how to

make it give me cash in the future, I should treat it as if it knows that sort

of thing.

It’s difficult to be rigorous about whether a machine really ‘knows’, ‘thinks’,etc., because we’re hard put to define these things. We understand human

mental processes only slightly better than a fish understands swimming.

Current AI approaches to ascribing specific mental qualities use the sym-

bolism of mathematical logic.

In that symbolism, speaking technically, a

suitable collection of functions and predicates must be given. Certain for-

mulas of this logic are then axioms giving relations between the concepts

and conditions for ascribing them. These axioms are used by reasoning pro-

grams as part of the process whereby the program decides what to do. The

formalisms require too much explanation to be included in this article, but

some of the criteria are easily given in English.

Beliefs and goals are ascribed in accordance with the the principle of ra-

tionality. Our object is to account for as much behavior as possible by saying

the machine or person or animal does what it thinks will achieve its goals. It

is especially important to have what is called in AI an epistemologically ade-

quate system. Namely, the language must be able to express the information

our program can actually get about a person’s or machine’s ‘state of mind’

— not just what might be obtainable if the neurophysiology of the human

or the design of the machine were more accessible.

In general we cannot give definitions, because the concepts form a system

that we fit as a whole to phenomena. Similarly the physicist doesn’t give a

definition of electron or quark. Electron and quark are terms in a complicated

theory that predicts the results of experiments.

Indeed common sense psychology works in the same way. A child learns

to ascribe wants and beliefs to others in a complex way that he never learns

to encapsulate in definitions.

Nevertheless we can give approximate criteria for some specific properties

relating them to the more implicit properties of believing and wanting.

Intends — We say that a machine intends to do something if we can

regard it as believing that it will attempt to do it. We may know something

that will deter it from making the attempt. Like most mental concepts,

intention is an intermediate in the causal chain; an intention may be caused

by a variety of stimuli and predispositions and may result in action or be

frustrated in a variety of ways.

Tries — This is important in understanding machines that have a variety

of ways of achieving a goal including possibly ways that we don’t know about.

If the machine may do something we don’t know about but that can later

be explained in relation to a goal, we have no choice but to use ‘is trying’ or

some synonym to explain the behavior.

Likes — As in ‘A likes B’. This involves A wanting B’s welfare. It requires

that A be sophisticated enough to have a concept of B’s welfare.

Self-consciousness — Self-consciousness is perhaps the most interesting

mental quality to humans. Human self-consciousness involves at least the


  1. Facts about the person’s body as a physical object. This permits reasoning from facts about bodies in general to one’s own. It also permits

    reasoning from facts about one’s own body, e.g.

    its momentum, to corre-

    sponding facts about other physical objects.

  2. The ability to observe one’s own mental processes and to form beliefs and wants about them. A person can wish he were smarter or didn’t want a


  3. Facts about oneself as a having beliefs, wants, etc. among other similar beings.

    Some of the above attributes of human self-consciousness are easy to

    program. For example, it is not hard to make a program look at itself, and

    many AI programs do look at parts of themselves. Others are more difficult.

    Also animals cannot be shown to have more than a few. Therefore, many

    present and future programs can best be described as partially self-conscious.

    Suppose someone says, ‘The dog wants to go out’. He has ascribed the

    mental quality of wanting to the dog without claiming that the dog thinks

    like a human and can form out of its parts the thought, ‘I want to go out’.

    The statement isn’t shorthand for something the dog did, because there

    are many ways of knowing that a dog wants to go out. It also isn’t shorthand

    for a specific prediction of what the dog is likely to do next. Nor do we

    know enough about the physiology of dogs for it to be an abbreviation for

    some statement about the dog’s nervous system. It is useful because of its

    connection with all of these things and because what it says about the dog

    corresponds in an informative way with similar statements about people. It

    doesn’t commit the person who said it to an elaborate view of the mind of a

    dog. For example, it doesn’t commit a person to any position about whether

    the dog has the mental machinery to know that it is a dog or even to know

    that it wants to go out. We can make similar statements about machines.

    Here is an extract from the instructions that came with an electric blan-

    ket. “Place the control near the bed in a place that is neither hotter nor

    colder than the room itself. If the control is placed on a radiator or radiant

    heated floors, it will ‘think’ the entire room is hot and will lower your blanket

    temperature, making your bed too cold. If the control is placed on the window

    sill in a cold draft, it will ‘think’ the entire room is cold and will heat up your

    bed so it will be too hot.”

    I suppose some philosophers, psychologists, and English teachers would

    maintain that the blanket manufacturer is guilty of anthropomorphism and

    some will claim that great harm can come from thus ascribing to machines

    qualities which only humans can have. I argue that saying that the blanket

    thermostat ‘thinks’ is ok; they could even have left off the quotes. Moreover,

    this helps us understand how the thermostat works. The example is ex-

    treme, because most people don’t need the word ‘think’ to understand how

    a thermostatic control works. Nevertheless, the blanket manufacturer was

    probably right in thinking that it would help some users.

    Keep in mind that the thermostat can only be properly considered to

    have just three possible thoughts or beliefs. It may believe that the room is

    too hot, or that it is too cold, or that it is ok. It has no other beliefs; for

    example, it does not believe that it is a thermostat.

    The example of the thermostat is a very simple one.

    If we had only

    thermostats to think about, we wouldn’t bother with the concept of belief

    at all. And if all we wanted to think about were zero and one, we wouldn’t

    bother with the concept of number.

    Here’s a somewhat fanciful example of a machine that might someday be

    encountered in daily life with more substantial mental qualities.

    In ten or twenty years Minneapolis-Honeywell, which makes many ther-

    mostats today, may try to sell you a really fancy home temperature control

    system. It will know the preferences of temperature and humidity of each

    member of the family and can detect who is in the room. When several are in

    the room it makes what it considers a compromise adjustment taking account

    who has most recently had to suffer having the room climate different from

    what he prefers. Perhaps Honeywell discovers that these compromises should

    be modified according to a social rank formula devised by its psychologists

    and determined by patterns of speech loudness. The brochure describing how

    the thing works is rather lengthy and the real dope is in a rather technical

    appendix in small print.

    Now imagine that I went on about this thermostat until you were bored

    and you skipped the rest of the paragraph. Confronted with an uncomfort-

    able room you form any of the following hypotheses depending on what other

    information you had.

  4. It’s trying to do the right thing, but it can’t because the valve is stuck. But then it should complain.

    room hot in case he comes in.

  5. It regards Grandpa as more important than me, and it is keeping the
  6. It confuses me with Grandpa.
  7. It has forgotten what climate I like. A child unable to read the appendix to the user’s manual will be able

    to understand a description of the ‘climate controller’ in mental terms. The

    child will be able to request changes like ‘Tell it I like it hotter’ or ‘Tell it

    Grandpa’s not here now’. Indeed the designer of the system will have used

    the mental terms in formulating the design specifications.

    The automatic teller is another example.

    It has beliefs like, ‘There’s

    enough money in the account,’ and ‘I don’t give out that much money’. A

    more elaborate automatic teller that handles loans, loan payments, traveler’s

    checks, and so forth, may have beliefs like, ‘The payment wasn’t made on

    time,’ or, ‘This person is a good credit risk.’

    The next example is adapted from the University of California philoso-

    pher John Searle. A person who doesn’t know Chinese memorizes a book of

    rules for manipulating Chinese characters. The rules tell him how to extract

    certain parts of a sequence of characters, how to re-arrange them, and how

    finally to send back another sequence of characters. These rules say nothing

    about the meaning of the characters, just how to compute with them. He is

    repeatedly given Chinese sentences, to which he applies the rules, and gives

    back what turn out, because of the clever rules, to be Chinese sentences that

    are appropriate replies. We suppose that the rules result in a Chinese conver-

    sation so intelligent that the person giving and receiving the sentences can’t

    tell him from an intelligent Chinese. This is analogous to a computer, which

    only obeys its programming language, but can be programmed such that one

    can communicate with it in a different programming language, or in English.

    Searle says that since the person in the example doesn’t understand Chinese

    — even though he can produce intelligent Chinese conversation by following

    rules — a computer cannot be said to ‘understand’ things. He makes no dis-

    tinction, however, between the hardware (the person) and the process (the

    set of rules). I would argue that the set of rules understands Chinese, and,

    analogously, a computer program may be said to understand things, even if

    the computer does not. Both Searle and I are ignoring practical difficulties

    like how long it would take a person with a rule book to come up with a


    Daniel Dennett, Tufts University philosopher, has proposed three atti-

    tudes aimed at understanding a system with which one interacts.

    The first he calls the physical stance. In this we look at the system in

    Its parts

    terms of its physical structure at various levels of organization.

    have their properties and they interact in ways that we know about.


    principle the analysis can go down to the atoms and their parts. Looking at

    a thermostat from this point of view, we’d want to understand the working of

    the bimetal strip that most thermostats use. For the automatic teller, we’d

    want to know about integrated circuitry, for one thing. (Let’s hope no one’s

    in line behind us while we do this).

    The second is called the design stance. In this we analyze something in

    terms of the purpose for which it is designed. Dennett’s example of this is

    the alarm clock. We can usually figure out what an alarm clock will do,

    e.g. when it will go off, without knowing whether it is made of springs and

    gears or of inegrated circuits. The user of alarm clock typically doesn’t know

    or care much about its internal structure, and this information wouldn’t be

    of much use. Notice that when an alarm clock breaks, its repair requires

    taking the physical stance. The design stance can usefully be applied to a

    thermostat — it shouldn’t be too hard to figure out how to set it, no matter

    how it works. With the automatic teller, things are a little less clear.

    The design stance is appropriate not only for machinery but also for the

    parts of an organism. It is amusing that we can’t attribute a purpose for the

    existence of ants, but we can find a purpose for the glands in an ant that

    emit a chemical substance for other ants to follow.

    The third is called the intentional stance, and this is what we’ll often

    need for understanding computer programs.

    In this we try to understand

    the behavior of a system by ascribing to it beliefs, goals, intentions, likes and

    dislikes, and other mental qualities. In this stance we ask ourselves what the

    thermostat thinks is going on, what the automatic teller wants from us before

    it’ll give us cash. We say things like, ‘The store’s billing computer wants me

    to pay up, so it intends to frighten me by sending me threatening letters’.

    The intentional stance is most useful when it is the only way of expressing

    what we know about a system.

    (For variety Dennett mentions the astrological stance. In this the way to

    think about the future of a human is to pay attention to the configuration of

    the stars when he was born. To determine whether an enterprise will succeed

    we determine whether the signs are favorable. This stance is clearly distinct

    from the others — and worthless.)

    It is easiest to understand the ascription of thoughts to machines in cir-

    cumstances when we also understand the machine in physical terms. How-

    ever, the payoff comes when either no-one or only an expert understands the

    machine physically.

    However, we must be careful not to ascribe properties to a machine that

    the particular machine doesn’t have. We humans can easily fool ourselves

    when there is something we want to believe.

    The mental qualities of present machines are not the same as ours. While

    we will probably be able, in the future, to make machines with mental qual-

    ities more like our own, we’ll probably never want to deal with machines

    that are too much like us. Who wants to deal with a computer that loses

    its temper, or an automatic teller that falls in love? Computers will end

    up with the psychology that is convenient to their designers — (and they’ll

    be fascist bastards if those designers don’t think twice). Program designers

    have a tendency to think of the users as idiots who need to be controlled.

    They should rather think of their program as a servant, whose master, the

    user, should be able to control it. If designers and programmers think about

    the apparent mental qualities that their programs will have, they’ll create

    programs that are easier and pleasanter — more humane — to deal with.


    Dennett, Daniel (1981).True Believers: the Intentional Strategy and Why

    it Works, The Herbert Spencer Lectures, A. Heath (ed.), Oxford University

    Press. This non-technical article describes the physical, design and inten-

    tional stances in philosophical language.

    Kowalski, Robert (1979). Logic for Problem Solving, New York: North Hol-

    land. This book describes the use of logical formalism in artificial intelligence.

    McCarthy, John (1979). Ascribing Mental Qualities to Machines1 in Philo-

    sophical Perspectives in Artificial Intelligence, Ringle, Martin (ed.), Human-

    ities Press. This is the technical paper on which this article is based.

    McCarthy, John (1979). First Order Theories of Individual Concepts and

    Propositions,2 in Michie, Donald (ed.) Machine Intelligence 9, Ellis Hor-

    wood. (Reprinted in this volume, pp. 000–000.) This paper uses the mathe-



    matical formalism of first order logic to express facts about knowledge.

    Newell, Allen (1982). The Knowledge Level, Artificial Intelligence, Vol. 18

    No.1, pp. 87–127. This article clearly expounds a different approach to

    ascribing mental qualities.

    Searle, John (1980). Minds, Brains and Programs, Behavioral and Brain

    Sciences, Vol.3 No. 3, pp. 417–424. This article takes the point of view that

    mental qualities should not be ascribed to machines.

    /@steam.stanford.edu:/u/ftp/jmc/little.tex: begun 1996 May 14, latexed 1996 May 14 at 1:40 a.m.