Why there are three eigenmodes

I previously introduced the family, village and city-level eigenmodes of society. What differentiates these societies is the relative probability of meeting friends, acquaintances and strangers.

• At the family-level people deal almost exclusively with friends. Encounters with people that could be regarded as acquaintances or strangers are rare.
• At the village-level people, if not friends, are at least acquaintances. Encounters with strangers from outside the village are rare.
• At the city-level people, most people are mutual strangers and encounters with strangers are normal.

Since even in the city people have acquaintances and friends, the village and family are actually subsets of the city eigenmode. People who live in city-level societies also belong to village-level and family-level societies. (This need not be a literal village; the 'village' may consist of a neighbourhood or a group of co-workers in a company.) Similarly, people in village-level societies also routinely experience the family-level.

The relationship between scale and the different eigenmodes can be attributed to the fact that maintaining acquaintanceships and especially friendships requires an investment of time, yet people's time is limited. If they encounter thousands of people over the course of a year, they cannot really be acquaintances let alone friends of all of them.

The number of friends a person may have is from about ten to about fifty (remembering that 'friends' in the technical sense includes close relatives). The number of acquaintances may be from about a hundred up to about a thousand. All other relationships are strangerships.

As the society's scale (interactions per unit time) changes, the proportion of friendships, acquaintanceships and strangerships changes as shown in the following figure.

• When scale is very low and people spend all their time with say ten others, all relationships will be friendships. Friendships=100%, acquaintanceships=0%, strangerships=0%.
• As scale increases and people each maintain say a hundred relationships, ten of those relationships will be friendships and the other ninety acquaintanceships. Friendships=10%, acquaintanceships=90%, strangerships=0%.
• As scale increases further and people each maintain say a thousand relationships, ten of those will be friendships, a hundred acquaintanceships, and the other 890 strangerships. Friendships=1%, acquaintanceships=10%, strangerships=89%.

Thus, as scale varies, one passes from a friendship-dominated society to an acquaintanceship-dominated and then strangership-dominated society. Since friends, acquaintances and strangers behave towards each other in different ways, the type of relationship that dominates a society determines the type of behaviour that is characteristic of that society.