Rectangles symbolize concepts.
Example: “Explain”, “Speak”, “Mouse”.
Arrows symbolize cause-effect relations.
The thicker an arrow is the stronger is correspondent cause-effect relation.
Cause-effect relation between “Explain” and “Speak” is strong.
Cause-effect relation between “Noise” and “Enjoy” is weak.
Usually (but not necessary) in the main memory all concepts are parts of one huge graph. However it is always possible to pick out a small sub-hierarchy which is highly cohesive with any given concept.