by John Allen Paulos
Several years ago the Nobel committee selected two economists, Thomas Schelling of the University of Maryland and Robert Aumann of Hebrew University, to receive the prize for their stellar work on game theory. Aumann has contributed many seminal ideas with real-world applications, one in particular that is especially relevant today. It concerns the notion of “common knowledge,” which is crucial in understanding many phenomena from the stock market, family dynamics, and, most topically, to the present situation with President Joe Biden.
First the terms. A bit of information is deemed “common knowledge” among a group of people if all parties know it, know that the others know it, know that the others know they know it, and so on. It is much more than “mutual knowledge,” which requires only that the parties know the particular bit of information, not that they be aware of the others’ knowledge of it
Consider now the dynamic and often mysterious relations among extended families, networks of friends, and business colleagues, the open secrets that people know while remaining ignorant of others’ knowledge of the same. This is a nice illustration, among many, of the difference between mutual knowledge and common knowledge.
Once a bit of mutual knowledge becomes common knowledge, however this transition comes about, the revelation often leads to a drastic re-evaluation of the situation and a desire for some sort of action. This is certainly true with families, friends. and colleagues who finally share a common knowledge about some previously shadowy suspicions.
The relevance of this to Joe Biden and the Democrats’ situation is clear. Many people who have met the President in recent months have come away with private doubts and concerns about his future candidacy but remained unaware that many others had a similar uneasiness. Biden’s abysmal debate performance ended that, as millions of viewers became aware of his likely vulnerability during the upcoming campaign and possible further decline over the next four years. The result of this transition from mutual knowledge to common knowledge is the widespread call for the president to bow out and allow an arguably stronger candidate to take over with a presumed better chance to defeat Donald Trump. Read more »