The “Streetlight Effect”: a metaphor for knowledge and ignorance

Here’s the beginning of my latest 3QD piece:

There is a story that I think anyone interested in human knowledge ought to know. It comes in many forms. Here is one version, incarnated as a joke: ‘A policeman sees a drunk man searching for something under a streetlight and asks what the drunk has lost. He says he lost his keys and they both look under the streetlight together. After a few minutes the policeman asks if he is sure he lost them here, and the drunk replies, no, that he lost them in the park. The policeman asks why he is searching here, and the drunk replies, “this is where the light is.”‘muttjeff01

A parable featuring the Seljuk Sufi mystic Nasrudin Hodja may be the earliest form of the story: ‘Someone saw Nasrudin searching for something on the ground. “What have you lost, Mulla?” he asked. “My key,” said the Mulla. So they both went down on their knees and looked for it. After a time the other man asked: “Where exactly did you drop it?” “In my own house.” “Then why are you looking here?” “There is more light here than inside my own house.”‘ The Indologist Wendy Doniger quotes this parable in her book The Hindus: An Alternative History, as a way to prepare the reader for the disappointing realization that the “available light” on Hinduism — the hymns, the histories, the archaeological remains — tends to illuminate the perspectives of dominant groups, relegating to the shadows the viewpoints of women, lower castes, and other marginalized groups.

Noam Chomsky has a characteristically dry and precise version of the story: “Science is a bit like the joke about the drunk who is looking under a lamppost for a key that he has lost on the other side of the street, because that’s where the light is. It has no other choice.”

So historians, mystics, scientists and drunks have something in common: they all tend to seek the truth where the process of seeking is easy, rather than where truth is. Responses to this problem vary. The mystic is most likely trying to remind the listener of how limited human knowledge is, and how often we look for solutions in precisely the wrong places. The humanities professor Doniger uses the problem as a justification for reading between the lines: using the available light to speculate about what may lie in the darkness. And the cognitive scientist Chomsky seems to be using the problem to justify why scientists answer questions that are almost, but not quite, entirely unlike the questions they originally set out to answer.

I’m a scientist, a history buff, and also a bit of a mystic, so I tend to combine all three perspectives on the “available light” problem, also known as the “streetlight effect“.

Read the rest at 3 Quarks Daily.

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About Yohan

I'm a neuroscience postdoc at the Neural Systems Laboratory in Boston University. My PhD was in Cognitive and Neural Systems, and my work involves computational neural network modeling, mostly of cognitive-emotional interaction. Apart from neuroscience, I spend a lot of time engaging with music, history, politics, philosophy, and religion.
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