Why you shouldn’t ask “why”

One major pastime for grad students is complaining about how bad our undergrads are (they, I’m sure, complain about us—I know I did when I was their age). They aren’t perfect, but sometimes their missteps can actually be enlightening.

In the most recent lab I graded, they generated this plot:
2 strains of bacterial growth
And then we asked them to consider why the two lines were parallel, even though the growth rate of the two states of bacteria (which can interconvert) are so different. One of the responses was: “because the population sizes are increasing at the same rate”. To which I whacked my head on my desk, and wrote in “yes, but why are they increasing at the same rate?”.  

I’ve been thinking about it more over the last couple days, and I realized the problem is not with the student, but with the question. “Why” tends to be too broad, with many possible answers. Unless the person you’re asking is interested in the exact same things you are, and even possibly in the same mood, they might then answer the “why” question with a totally different (though equally correct) answer.

An example

Why do we have eyes on our heads and not our hands?

I could answer this question by saying “on day N of development, transcription factor X is expressed in the proto-cephalic ectoderm, which activates eye genes A, B, and C. X is not expressed in the limb tissues, so genes A, B, and C aren’t expressed there.” Lately, that’s more the kind of thinking that I’ve been looking for in the problems I’ve been thinking about.

Of course, you might have been looking for an answer more like, “while being able to move your eyes rapidly and in a wide range of motion is useful, the time delay in getting the visual information to your brain negates that advantage, and your hands are too exposed to injury”, and that’s also a totally valid answer to the question. (As is: because it would be really creepy).

So when we ask undergrads (or, really anyone else) a “why” question, we’re expecting them to be able to know which of those answers we’re looking for.


I suspect its true that every “why” question (at least about things in the natural world, which don’t generally have agency like people) could instead be rephrased as more than one “who/what/when/where” question. In the examples above, they might be “what are the mechanistic causes of eye formation that are differentially present in the head and hands” and “what are the evolutionary disadvantages of having eyes in the hands”. And if you really want to ask one of those questions, why not just ask it and save your reader from trying to divine which one you meant.

The process of figuring out which one you meant is useful not only for your reader, in saving them from thinking of the wrong thing (and, if it’s graded, from losing points answering the wrong question), but for yourself as well. Asking yourself what other question your “why” question is isomorphic to means that you have to think clearly about your question. Those familiar with the Feynman Problem Solving Algorithm (1. Write down the question; 2. think really hard; 3. write down the answer) will recognize that starting to think really hard means you’re almost 2/3 of the way through!

It’s okay to start your thinking on a problem by asking why—chances are the really deep and interesting questions are most simply put as a “why”. But as you think harder about the question rephrase, you should continually be rephrasing it, trying to figure out what kind of answer you’re looking for.

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