they are integrated in a taxonomy, a general classification of
animals and plants. The terms that designate natural species are
mutually exclusive—a given animal does not belong to two
classes—and jointly exhaustive—all animals are assumed to
belong to one such class. Note that this is not true of kind-con-
cepts outside of the natural domain. A piano can be both furni-
ture and a musical instrument (thus the kind-concept "piano" is
a member of two higher-level classes). Also, natural kind terms
are grouped into larger classes that correspond to general
body-plans, such as "birds," "mammals," "insects," etc.^12
Why do some things move of their own accord?As I said above, [109]
dots on a screen can give the impression of chasing each
other rather than just colliding, if we adjust their motion in
subtle ways, and even infants seem sensitive to this differ-
ence. A while ago, psychologist Alan Leslie showed that
infants too fell prey to Michotte's causal illusion, distin-
guishing between displays where adults see causes and dis-
plays where they do not. Another child psychologist,
Philippe Rochat, used this kind of experimental set-up with
six-month-olds and showed that they too are sensitive to the
difference between "physical causation" (push, pull, hit) and
"social causation" (chase, avoid). So it would seem that all
these connections between events are somehow represented
much earlier than we thought: certainly before the child has
acquired the concepts "chase" or "avoid" and before she has
any experience of either. Older children, say around three,
have definite expectations about the difference between self-
propelled and non-self-propelled objects in the environ-
ment. For instance, psychologist Rochel Gelman tested
preschoolers on whether a series of animals and statues of
animals could move. To her subjects it was quite clear that
real animals could move of their own accord but that statues
could not. Children have this intuition but they have no
explanation for it. Some of Gelman's subjects explained that
the statue could not move "because it had no legs." When
shown that the statue did have legs, they argued that "these
were not good legs," and so on. This often happens when
testing such deep intuitive principles. Children have the
principle, they have the systematic intuitions, yet they have
no explanations for them. This is because the intuition is
THEKIND OF MIND ITTAKES