THE WELL-DESIGNED CHILDJohn McCarthy

Stanford University

jmc@cs.stanford.edu

http://www-formal.stanford.edu/jmc/September 28, 2007

• • The world into which a human is born is complex. W
• discuss some of the complexities, concentrating on one—
• 3-d semi-permanent, movable objects.
• • Evolution has equipped a baby with some innate kno
• edge of the world. That works better than starting as
• blank slate.
• • Consider a well-designed logical robot child (WDC).
• Mostly it will have the innate abilities we conjecture real
• children have, but sometimes we can do better. THE LOCKEAN BABY
• • John Locke 1693: The baby starts out as a blank slate.
• It builds its knowledge by inferring associations among
• stimuli.
• • Since 1950 people proposed to start with a Lockean
• blank slate baby machine and have it learn from its exp
• rience.
• • Starting from the blank slate, I’ll bet it’s a lengthy
• process to infer the existence of 3-d objects. I don’t- think anyone has made an AI system that can do it.
• • A billion years of evolution has provided us with prett
• good prejudices about the world far better than a blank
• slate. Our robot child should also have them THE WORLD IS COMPLICATED- • The world’s structure is not directly describable in terms
• of the input-output relations of a person. The basic struc-
• ture of the world involves elementary particles on time
• scales of 10−25 seconds, but intelligence only evolved
• structures of more than 1023 elementary particles.
• • Even at the level at which a small child can perceive
• the world is extremely complicated. Here are some of
• complications.
• • Reality and appearance Animals and humans don’t p
• ceive the structure of our environment directly. Senses
• have evolved to give partial information about objects- and their relations.
• • The world is 3-d, but our senses react to surfaces. MORE COMPLICATIONS
• • semi-permanent objects Much of the world consists
• three-dimensional objects that have masses, moments,
• compliances, hardnesses, chemical composition, shap
• outer surfaces with textures and colors, are often made
• identifiable parts which sometimes move relative to each
• other. A particular object can disappear from perception
• and reappear again.
• Note that the structure and location of an object in
• world are more persistent than its appearance and lo
• tion in the visual field or relative to the hands.
• • temporal structure The environment of a child has
• complex temporal structure. Some items change in sec-
• onds, others last for hours, days, or years. Babies
• in the present. The concepts of tomorrow and yesterda
• are not learned right away.
• • causality Events cause changes in objects and their
• lations and cause other events. STILL MORE COMPLICATIONS- • solidity Objects are solid and do not ordinarily penetrate
• one another. Some are rigid and some are flexible.
• • gravity Unsupported objects fall to a lower surface.
• • kinds of objects Objects have kinds, and objects
• the same kind have properties associated with the kind.
• Babies are ready very early to learn what kinds there a lemons, belong to natural kinds. The objects of- • natural kinds Many of the objects a child encounters,
• e.g.
• natural kind have yet undiscovered properties in common.
• Therefore, a natural kind is not definable by an if-and-
• only-if sentence formulated in terms of observables.
• • relations Objects not only have individual properties
• and belong to kinds, but objects and kinds have relations
• with one another. At least some ternary relations such
• as betweenness are basic. Also “A is to B as C is to
• seems to be basic. In its numerical use, it reduces- the equality of two fractions, but the quaternary relation
• seems to be basic in common sense usage. WHAT DO BABIES KNOW AND WHEN?- • Q: If the world is so complicated, how can babies
• anything purposeful?
• • A: They know simple cases of phenomena.
• • There’s good psychological evidence that they have
• innate knowledge of solid objects that continue existing
• even when out of sight. How do they remember an object
• that has gone out of sight so as to recognize it when
• reappears?
• • They are ready to ascribe purposeful action to humans
• and animals and to try to influence them.
• • the principle of mediocrity (from the astronomers) Our
• child is like other children. This lets it reason in b
• directions.
• • persons Some objects are animate and have purposes
• analogous to those of the child. They can be influenced
• but are sometimes to be feared. Defects in innate under-
• standing of persons, e.g. autism, harm the child. WHAT DO WE WANT IN A WELL-DESIGNEDROBOT CHILD?
• • Distinguish appearance from reality
• • natural kinds Natural kinds don’t have if-and-only-if def-
• initions. There may always be more properties to
• learned. To a small child, all kinds are natural. The
• robot child should think in terms of natural kinds.
• • three-dimensional objects These are more stable than
• the perception of them by any sense.
• • perceive motion as continuous
• • actions and their effects
• • recognize parts Recognize parts of an object and their
• relations to the others. It would be interesting to have
• grammar of 3-d physical structure analogous to that
• sentences.
• • focussed curiosity
• • grammar of goal regression To do A, I need to do
• first, and to do B, I need to do C first.
• • introspection Children begin to do this by age 3, do
• well by age 5. The WDC needs it. THE SPELKE EXPERIMENT- This psychological experiment exhibits abilities of human
• babies we want in the WDC.
• Elizabeth Spelke described a number of experiments that
• she and others did to discover and verify innate mental
• abilities. The technique uses the fact that a baby
• look longer at something surprising than at something
• that seems familiar.
• Here’s one that was first done in 1973 and was repeated
• by Spelke in 1993 with two months old babies. There
• are experimental babies and control babies and the
• periment has two phases.
• babies are shown nothing. The experimental babies In the first phase the control- an object go behind a screen and shortly another object
• emerges on the other side of the screen. The timing
• such as would be appropriate if the first object struck
• the second object and knocked it from behind the screen.
• The babies are shown the phenomenon enough times
• get bored with it and stop paying attention.
• In the second phase of the experiment the screen is
• moved. There are two variants. In the first variant,
• first object strikes the second and knocks it onward.
• the second variant the first object stops short of the sec-
• ond, but the second object takes off as though it had
• been struck. The control babies look at both variants
• the same amount of time. The experimental babies lo
• longer at the second variant.
• The conclusion is that the experimental babies inferred
• that the first object had struck the second when the event
• occurred behind the screen. When the screen was
• moved, they were not surprised when the expected event
• was shown to occur but were surprised and looked longer
• when this expectation was not met.
• The conclusion is that babies have innate expectations
• about dynamics. For details see Spelke’s 1994 article
• Cognition, Initial knowlege: six suggestions. THE WELL-DESIGNED CHILD AS A LOGICALROBOT
• • Not even a sketch of a design—just some ideas.
• • Appearance and reality
• Appears(appearance, object) is too simple except in a lim-
• ited context, but children think in limited contexts.
• Holds(Appears(person, appearance, object), s) says more
• is suitable for referring to the child from the outside. CONTEXTS
• • The correctness of a child’s beliefs and references
• objects depends on context. Children change context
• frequently.
• • When looking at a child’s ideas from the outside,
• can use the theory of contexts as objects introduced
• my Notes on formalizing context. In that theory Ist(c, p
• true if the proposition p holds in the context c. V alue(c,
• is the value of the expression exp, e.g. Color(Block1),
• context c.
• • V alue(Belief s(Child1, S0), Color(Block1)) = Red asserts
• that in the context of Child1’s beliefs in situation s, Blo
• is red. The context theory lets us enter the context
• Belief s(Child1, S0). Then we have Color(Block1) = R THREE CHALLENGES AND A CONCLUSION- • Make a robot baby that can do the Spelke experiment
• honestly. But what’s honestly? It may start knowing
• about collisions and knowing about occluded objects,
• at least it shouldn’t start with knowledge combining
• two.
• • Its contexts should change like those of a baby.
• • It should properly relate 2-d appearances to 3-d realit
• and also relate tactile appearances to reality. Here’s
• puzzle.
• • What babies know presents challenges to AI—to AI
• all schools.
• • This talk is partly based on the manuscript
• http://www-formal.stanford.edu/jmc/child.html.