The Detection of Purpose

Contents

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What to Do

Spend a moment and watch the three squares move around the screen.

One of these squares is actively controlling its movements; it has the purpose of tracing out a particular pattern of movement. The other two squares have no purpose; they move as they do because they are being pushed around by external forces.

Notice that it is impossible to tell, by looking at the behavior of the three squares, which square is moving purposefully and which are not. You can find out which is the purposeful square by applying a disturbance to all three squares using the mouse. The square with a purpose will resist these disturbances; the purposeless squares will not resist. This means that you can detect the square that is moving purposefully by looking for the square that is influenced least by mouse movements.

In this demonstration you are using The Test for the Controlled Variable to determine which of the three squares is controlling its movements. The square that is controlling its movements is behaving with the purpose of making a particular pattern of movement and resists disturbances to that pattern. The demonstration shows that you can't tell whether a behavior (such as a movement pattern) is purposeful without doing The Test to determine whether that behavior is under control.

Once you think you have detected the purposeful square you can press the mouse button (the cursor can be anywhere on the screen) and the actual purposeful square will be "filled in". Press the mouse button again and a new square (possibly the same square as before) will become the purposeful square and all squares will become unfilled. You can then try to find the new purposeful square.

What To Notice

Notice that that the movements of all three squares appear quite lively; there is nothing that distinguishes the appearance of purposeful from that of purposeless (mechanical) behavior. The only way to distinguish purposeful from purposeless behavior is by doing The Test to determine whether a variable (in this case, the pattern of movement around the screen) is under control.

What Works Best

It may not be easy to tell which square is resisting your disturbances (mouse movements), especially if you use abrupt mouse movements to disturb the squares. It's best to disturb the squares using relatively slow mouse movements that follow a fixed pattern, such as a circle. Notice that two of the squares will follow this pattern of mouse movements to some extent (the squares are also being pushed around by a disturbance generated by the computer -- the disturbance that keeps them moving when you are not moving the mouse -- so they won't follow the pattern of mouse movements exactly). Notice also that one of the squares seems to "do its own thing". This is the square that is protecting its movements from your disturbance.