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.


By Yohan

I'm a Research Assistant Professor at the Neural Systems Laboratory in Boston University. My PhD was in Cognitive and Neural Systems, and my work involves computational neural network modeling of cognitive-emotional interaction and psychiatric disorders. My bachelor's and master's degrees were in physics.

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

My mother, a dementia patient went missing for 18days. We looked high and low for her. Extensively searched for. her. We ultimately found her in a mental health institution, the only one we hadn’t searched as we didn’t expect she’d have gone so far. Meanwhile my brother had a dream that my mother was roaming around in a disoriented state on the roads with the hands of God protecting her from the sky n with us rounding up together with ours back to her , searching for her somewhere else.

Here is my new born story from Mulla Nasrudin’ s Streetlight story;
A neighbour saw Mulla Nasrudin searching for something on the ground under a streetlight. “What are you searching for, Mulla?” he asked. “For something interesting,” said the Mulla. Somewhat puzzled but hopeful, the neighbour went down on his knees and started searching. After a while, the neighbour asked: “What have you found so far?” “A key someone must have lost, a nail which might be useful sometime and a piece of paper with some inscriptions which I need to decipher later,” replied the Mulla. “Why don’t you look over there also instead of spending your whole time here? You might still find more things over there!” “Oh, there is light here on this side. Over there it is dark, you wouldn’t see anything,” said the Mulla.

Our brain has two capacities; recognising patterns in nature (shared with all living beings) and for constructing patterns (shared with a few animals). Those two capacities have evolved mainly by natural selection to enable us to survive well by quickly recognising opportunities and avoiding dangers. But with the invention of language we have taken those two capacities to a very high level of complexity that goes beyond our immediate survival (in the same way the inventions of geometry and Algebra have taken mathematical thinking beyond mere counting) which enabled us to survive very well and to dominate the whole earth. Science is a systematic extension of these two capacities plus language (ordinary or mathematical) with added insistence on the need for rational thinking and evidence that can be confirmed by a large number of researchers of patterns. Now, this is the light on this side of the street where we have found natural laws and become able to construct cultures and technologies.

But what about the other side of the street where there is no light? Can we find somethings of interest over there also?

First, we need to acknowledge the possible existence of interesting things or knowledge on that other dark side. And second, by not insisting on investigating this other side with “pattern recognition + pattern construction + rational thinking + confirmed evidence” or science. We may have other capacities that have evolved in us epiphenomenally which we can use if we can disable our scientific mind for a while.

The koans’ trick in Zen which exhaust and incapacitate rational thinking, mindfulness and pure non-judgmental awareness of experiencing just ‘what is’ here and now, the whirling of Sufi dervishes, the controlled use of psychedelics, etc. all seem to open doors of perceptions that are not rational (but not irrational either) and lead to individual experiences that are transformative beyond what the capabilities of what we find under the streetlight. I am not saying that these are the ways we should go to investigate this other dark side. I just mention them in order not to end my comment without giving possible alternatives to scientific investigation for knowing what is out there and real.

Thank you for “Science is Symmetry” article. I enjoyed reading it; one of the best articles I have read on symmetry in physics. And by the way, I am a theoretical physicist but now retired from academia and in the business of establishing and managing schools.
All the best.

[…] 1.  The Forest Service, for historical reasons, has never sited much wind or solar energy, it’s mostly BLM. So if you were going to ask the question about wind and solar and transmission  NEPA, why would analyzing FS decisions even be relevant? Perhaps because PALS exists, and BLM doesn’t have an equivalent (perhaps this is an example of the streetlight effect). […]

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s