What makes our minds form many separate mental realms, instead of attempting, as scientists do, to see all aspects of the world in a unified way? Because, at least in everyday life, the latter simply isn't practical. Consider how different the rules are within the physical and social realms. If you want your furniture inside a different room, you normally would push it there. But when you want to move your party guests, it would be rude to push them there. Contrast the principles of physics and geometry with those we use in the social realm. In the physical realm, the rules seem very orderly:
-- A stationary object stays where it is unless another object pushes it. --- A moving object continues in its course until some external force makes it stop. ----All unsupported objects start to fall.
-----No two things can occupy the same location. -----Etc.
These principles seem clear to us — but infants cannot appreciate them until they've built up ways to represent ingredients like thing, shape, place, move, and near. It takes each child many years to develop these abilities.
Our comprehensions of social acts are based on different principles. When an ordinary object moves around, we usually see an obvious cause; most likely, another object pushed it. But when we see a person move, we rarely see the cause at all — because it's buried in a brain. In predicting how a person will react to an expression or gesture, we have little use for physical properties like color, shape, or place. Instead, we employ almost entirely different conceptions. To guess the outcome of a social interaction, we have to be able to represent each person's mental state — and to do that, we must develop concepts about traits, dispositions, motives, and plans. The concepts that serve so well for physical objects are of little help within the social realm — and vice versa.
When normal children start to talk, among the early aspects of their speech are words that distinguish animate things. Frequently, a child will use a single expression for all kinds of animals, and for everything else that can move by itself — for example, an automobile. According to our view of things, this surely is no accident.
To adults, the laws that govern the physical world seem simpler and more orderly than those that apply to human events. Does this mean that for infants, too, it should be easier first to master the physical world and later to proceed toward social and psychological understanding? No. Paradoxically, the social realm is initially the easier! Imagine that an infant wants a certain toy and that there's a sympathetic person near. The easiest thing is to make a request — that is, a gesture, smile, or cry — and this will probably achieve the goal. It would be far more difficult for the infant to coordinate all the complicated machinery for planning and executing the trajectory for propelling the object from where it is to where the infant wishes it to be. From the point of view of a physically helpless infant, the social realm is by far the simpler one.