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In a casual conversation amongst a well-established group of friends, themes are taken up for a period of time then abandoned for others, often to be taken up once again on some later occasion.
Metaphor
In society an issue may become fashionable for a period of time as the coin of exchange between opposing forces. It may then be abandoned in favour of some other issue, only to be taken up again on some later occasion.
[Features]The manner in which interest in the topic develops and declines to the point at which people are 'tired of it' and seek an alternative. How not discussing a topic for a period increases the interest with which it is taken up on a later occasion.
[Contrast]The reintroduction of issues for consideration by public opinion is very much under the control of the media (themselves possibly an instrument of government control).
[Keys]How new topics get introduced and how old topics get re-introduced or definitively rejected. How long a topic is discussed or remains undiscussed. How the level of interest in the conversation is maintained through shifting between contrasting topics.