The distinction of center/periphery is based on the stratified structure of ancient cities, where the Court or a temple is located in the center, residencies of bureaucrats or noblemen in the semi-periphery and merchants, craftsmen or farmers in the periphery. But sociologists usually use it non-geographically as the dichotomy that indicates the uneven distribution of capital as power in social systems.
1. center/periphery and essential/inessential
1.1. Essence in not always center.
In our body systems, brains are essential, while nails or hairs are inessential. Unlike the latter, the former is so essential that a body system cannot survive without it. But you cannot say a brain is the center and nails and hairs belong to the periphery of a body system, because the body system is different from the social system, where self-conscious agents, namely subsystems that can represent the height of capital as power select one another.
1.2. Center is not always essence
On the other hand, the privileged parasite classes in l’Ancient Regime before the French Revolution was the center to the periphery as the third estate, because they had high capital. However, they were not essential, as the social system could survive or better survive without those classes.
2. Selectors are selected
A social system reduces the indeterminacy of interdependent selection and individuals make themselves the selected being through selecting one another.
To give an example of applicants for admission to colleges, they set an criterion for selection, whose priority order forms the relation of center/periphery; the first choice is A college, the second is B, the third is C and so on. Although they think they just follow the established ranking, it is their decision which to enter, when they succeed in passing more than one college entrance examination, that decides the ranking. There is an autopoietic reflection between them.
Suppose an applicant turns out to fail to pass the examination of A College and succeed in passing the examination of B College. Then, he might say, "To tell the truth, I did not want to go to A College. B College is better than A." It is ressentiment. Although the desire of applicants decides the ranking of colleges, they decide the ranking of themselves through the very desire.
3. The structure of differentiation
Many social thinkers have considered the equal society as an ideal from ancient times. However, as long as people wish for the freedom of selection and try to satisfy the desire for difference, the center/periphery structure does not disappear. Though the information revolution has transformed the hierarchical society into the network society, it does not correct the maldistribution of capital as power. Rather, the gap between the rich and the poor has become still larger. The spatial metaphor to describe the stratification of the hierarchical society was top/bottom, while center/periphery is a metaphor more appropriate to describe that of the network society.