The Theater of the Absurd: The War Log Edition — Part 2

In the Google Age, it is hard not to take the easy way out and just google the answer to many a question which one could have otherwise enjoyed solving and learn a lot from the exercise. I hope that some gave at least a few brain cycles to figure out the puzzle mentioned in the post “The Theater of the Absurd: The War Log edition.” Here’s the follow up to that post.

The solution to the puzzle is in the wikipedia entry on “Common Knowledge.” You may wish to check it out before continuing with this post.

In that section of the entry for common knowledge in the wikipedia, it says,

“What’s most interesting about this scenario is that, for k > 1, the outsider is only telling the island citizens what they already know: that there are blue-eyed people among them. However, before this fact is announced, the fact is not common knowledge.”

I think that that is an incomplete explanation. I will go into what’s missing in a bit. For now, here’s how I like to think about common knowledge.

Imagine that I send you an email saying, “Roses are red.” Clearly, I know that roses are red. Perhaps you also know that roses are red. But I don’t know that you know that roses are red. Even after I send you the email, I still don’t know if you know that roses are red. Perhaps you have not read that email or maybe it was not delivered.

When you do read my email, you know that roses are red (if you did not know before) and you know that I know that roses are red. Now you send me an email saying “Thanks.” When I get that reply from you, I know that you know that roses are red, and that you know that I know that roses are red.

But you don’t know that I know that you know that roses are red. You only get to know that bit if I were to email you saying “Thanks for replying to my email about roses are red”, and you were to read that email.

To cut a long story short: only if we have an infinite number of back and forth emails does “Roses are red” become common knowledge with regards to you and I.

Now imagine that we are sitting in the same room intently watching TV. It’s a nature program and David Attenborough breathlessly declares that roses are red. I hear it and also note that you too heard that astonishing pronouncement. Now I know that roses are red; I know that you know that roses are red; I know that you know that I know that roses are red; . . . ad infinitum. No need for an infinite number of emails required in this case.

(Note that instead of David making that statement, either one of us could have said “roses are red” and it would have become common knowledge for us.)

General knowledge is when some information is known to all concerned. Common knowledge is when some information is not just known to all but all concerned also know that that information is known to all.

Coming back to the logic problem. Everyone knows that there are blue-eyed people in the village. There’s an exception. If there is only one blue-eyed person in the village, all she sees are brown-eyed people and so cannot know for sure if there is a blue-eyed person in the village or not.

When the visitor — perhaps David Attenborough there to make a documentary on people’s eye color — announces loudly before the entire assembled village that not all villagers are brown-eyed (meaning there is at least one blue-eyed villager), the fact becomes common knowledge. This means that all villagers know that all villagers know. It also means that if the village had only one blue-eyed resident, that resident now knows that there is a blue-eyed person in the village, and can now logically deduce her eye color.

Now here’s the interesting bit. Attenborough’s announcement did more than just make general knowledge about eye-color into common knowledge. It implicitly announced a “Day 1” for the logical process to get started and made that “Day 1” common knowledge. Why was this important? Because without a date on which to anchor the start of the logical deduction, it would not be possible for people to logically deduce their eye color if there were more than one person with blue eyes.

The thing to note is that the logical process of deduction requires a “coordinating signal” which says, “People, you may start figuring this one out from today.” It’s the coordinating signal function of Attenborough’s announcement that solves the problem.

All this is fine and interesting, you may say. But what does it have to do with economic development in general and with India’s economic development in particular, you may ask.

Everything, actually.

Economies have huge number of economic agents (individuals, households, firms) and in any complex economy larger than a one-person economy (aka Robinson Crusoe economy), there arise numerous coordination problems. Devices, associations, institutions, and various other methods have been invented to solve these coordination problems.

Money is one of them. So are markets. Communication channels too, the latest of which is the internets (or the web.) There’s eBay and Craigslist. There are institutions such as central banks, and constitutions, and political parties, and Olympic associations, etc. All of these and many more solve coordination problems.

Coordinating signals are necessary to make things happen. A society could have all the necessary bit to get something done but without a credible coordinating signal, it will not get done. Economies need the equivalent of coxswains in rowing, someone who “coordinates the power and rhythm of the rowers.”

I have pondered this matter of coordination and coordinating signals in the case of India’s development. Some years ago I figured out a simple model for the development of rural India, called RISC–Rural Infrastructure & Services Common. (Google RISC)

What RISC does is solve a coordination problem — that infrastructure providers find users missing, and users find infrastructure missing.

And now for the conclusion of this thread. In the post about wikileaks (same link as the one at the top of this post), I wrote “that what the wikileaks did by publishing the Afghan War Logs is that it made what was general knowledge into common knowledge.”

The US government knew what was in the wikileaks since it was their secret. They knew, for instance, that Pakistan was using American taxpayer money to kill American soldiers. Pakistani leaders knew that too. Many journalists and researchers also knew that. What wikileaks did was, first of all, to make that information more generally known. But more than that, it made the US leaders know that the American public knows, and the public knows that the US leaders know that the public knows.

The wikileaks also provided a coordinating signal of sorts for all to get started with solving the problem. Suddenly a lot of different people started looking at the problem thus compelling the US leadership to take action instead of pretending that all was hunky-dory.

As of CBS News puts it in his column, it’s “Time Start Demanding Answers From Pakistan“:

[Thanks to Rohit and others who commented or wrote to me about the logic puzzle and its solution.]

Author: Atanu Dey


7 thoughts on “The Theater of the Absurd: The War Log Edition — Part 2”

  1. The question is, why is US doing it, under both republicans and democrats? When Obama has to struggle for each dollar in spending against a lot of “new austerity” hawks, why would they blatantly look the other side when it comes to Pakistan? I wouldn’t agree that this is mere incompetence.


  2. I think one of the greatest leaders had minds of Lord to actually plot a deep, hidden, incomprehensible 50 year strategy in this war of terror thing. It was started by a cluless retard (I love this phrase Atanu) Bush and many corporations went on to mint hell lot of money and contributed major chunk to American treasury by way of taxes on corporatons, civilians and soldiers alike. Now if Obama were to declare tonight that he is pulling out all the troops from the hell hole of Afghan and Pak once and for all, the US economy will instantaneously swirrel down to conditions worse than the depression of early 30’s. The dead soldiers cost the Govt a lot less to the Govt..some gallantary awards, a memorial in his town and a pension fund for the survivors and that again is managed by the large insurance firms who recently went bankrupt. So now all the more reason to pump more soldiers and ammunition to the hell holes where practically there is nothing left to gain or loose except for a few lives who are not that significant for their respective Governments anyway. The US president is left with no alternative but to rant the stories of American Patriotism and the sacrifices made by his subjects. Such stories then inspire some more young minds to join US Army and Air Force and be posted in Pakistan.


  3. 1)I did solve the puzzle before posting :). But found better link to explain the solution.I had come across similar puzzle few years back but it was not in the context of Common Knowledge so it was just fun back then and now it makes sense.
    2)I understand the difference between the general knowledge and common knowledge but I am bit confused about the back and forth communication infinitely.
    What I am wondering , once I know roses are red, you know roses are red (you also know I know here as I told you), I know you know.., you know I know you know… As far as knowing roses are red is concerned we both know now and we both know that other knows. Why does further iteration makes difference when number of parties involved == 2 (as in this example).
    Is there any other practical example here to understand why these further iterations would be required ?


  4. I wouldn’t harp so much on “common knowledge” between the American administration and the people. “The people” are busy preserving what jobs they can and getting their sorry asses out of a financial quicksand over 50 years in the making, which is now nosediving because of the diminishing returns of pumping hydrocarbon steroids into a catatonic patient. Common knowledge is useful only if you have the potency to act on it. What are we doing about Dick Raju, Madhu Koda, Lalit Modi, the other Dick Modi, crore-garlanded Mayawati, spectrum Raja, and all else about who common knowledge abounds?


  5. If there are at least two people with blue eyes, everybody knows that there are blue eyed people without being explicitly told.
    In that case all that is required from the vistor is a statement ‘let this be the day1 for reasoning to begin’. He need not tell that he sees blue-eyed people.
    Let me know if you do not agree with my statement above.
    It has been two years but I cannot get this puzzle out of my head.


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