My 4-year-old asks me questions like "Why is water transparent?" What kind of "why" does he mean?:

  1. What sense does it make for water to be transparent?
  2. How is it achieved that water is transparent?

The first question would be more philosophycal and the second question more physical. I don't think I would be able to explain to him the difference between those type of questions.

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    "Well, you see, the electron energy levels happen to match up precisely so that when the photons hit the molecules [...]"
    – user541686
    Commented Jul 14, 2015 at 23:43
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    He means "When I say 'why', you tell me interesting stuff and I often learn a lot, so... 'why'" :)
    – Max
    Commented Jul 15, 2015 at 2:54
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    I agree with everything already said, and don't have enough to warrant a new answer. However, I want to say that 'Why' is good, and the more he asks it the better. Answering his questions not only helps him learn, but encourages him to learn and stay curious; which I consider even more important. To this day I still have fond memories of long car rides playing the 'why' game (when I was a little older and more articulate, but still same principle). The longer you can keep him asking why, and encourage it, the more your help him continue to learn and stay curious!
    – dsollen
    Commented Jul 15, 2015 at 13:04
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    So... What's the answer? Why is water transparent? Commented Jul 15, 2015 at 15:01
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    I have no idea. The reason I have to know what kind of why he asks is because I have to know who I have to call.
    – Mathias F
    Commented Jul 15, 2015 at 15:45

9 Answers 9


In my experience, he often doesn't know himself what he means. I've heard a lot of four-year-olds ask "Why?" ad infinitum -- sometimes it's just a way of saying, "Tell me more."

I would suspect that for most four-year-olds, asking "Why?" is a way of trying to learn more about the things around them, but I think that they are often looking for a simple explanation that doesn't necessarily answer the question they are technically asking.

"Why is water transparent?" could mean:

  • "What does transparent mean?"
  • "Why are some things transparent and others aren't?"
  • "How is it possible that I can see right through something?"
  • "Pay some attention to me, and make me feel like I'm important to you."

... or any number of other things.

If you give an answer to what you think is being asked, you can often tell if you're on the right track by how much the child engages your answer. If he seems interested in your answer, you're probably on the right track.

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    Welcome to the site, GentlePurpleRain. Good answers! I look forward to reading more of them. Commented Jul 14, 2015 at 18:05
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    Children also typically hit a moment where they comprehend that true ultimate causes are difficult to identify. Repeatedly asking "why" then becomes for a while a game where they wait for you to say "because God wills it", or "I don't know", or "it just is", knowing that you can't actually go on forever. Send them to Aristotle (en.wikipedia.org/wiki/Four_causes) Commented Jul 15, 2015 at 0:43
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    @Steve: As I have found out (after a few kids), there is a way to stop this "Why?" game: You just ask "Why what?", insisting on a correctly worded question. Of course, you having lost the child a couple of "Why?" questions back, when your answer got too sophisticated, the child won't know what to ask for. Then the two of you are back to you being able to give way more detailed answers than the child can handle, with which both of you can deal with: the child asks questions matching her knowledge of the world, and you give such answers. This worked splendidly for (the remainder of) my kids.
    – sbi
    Commented Jul 15, 2015 at 6:47
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    An anecdote: my five year old daughter was asking about the "holes in the moon" (craters) and I preempted her "why" game by dumping all the information I had about it up front. "Oh yeah! Those are craters, they're formed by meteorite strikes which are like tiny rocks in space that fly everywhere. They don't hit Earth because of our atmosphere..." and etc etc. Afterwards I ask, "Do you understand?" She sighs heavily in the backseat and utters in monotone, sounding defeated: "Now I know everything."
    – adsmith
    Commented Jul 15, 2015 at 16:02
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    @adsmith Ahh... I remember knowing everything... those were the days. ...then I moved out unto my own. I am not young enough to know everything. - Oscar Wilde
    – WernerCD
    Commented Jul 15, 2015 at 18:56

My experience is that, yes, first of all, a small child's "Why?" is usually "Please keep talking." However, I have also found that sometimes they do have particular questions, and that they learn to ask clearer questions if you help them realize that there are many possible questions.

While it probably won't work the first time, try offering them options about which question they want answered. ("What are you asking? Do you know what 'transparent' means? ... Do you want to know why we call it transparent, or what makes the water transparent? Or do you just want me to talk more about water?") Even just saying "I don't know how to answer 'why' here, but i'm happy to talk about transparency and how light works, if you want."

In general, a four-year-old probably understands a little more than you think, and can express a little more than you expect, if you help them. Of course, the goal is to get them to be clear on their own, so at some point you might offer less help, and just answer whichever one you like, and let them re-ask the question. Getting to that point, I have found direct conversation about the conversation to be very helpful.

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    Agreed, he's saying: "Please talk to me about the water and other interesting things related to the water, in addition, please engage with me because I'm in a mood to learn something." Commented Jul 16, 2015 at 11:27

If my son asked me why water was transparent, I'd honestly not be able to answer him. I think I'd have to say something like "I honestly don't know. Now you mention it, I'd like to know that myself. Shall we try and find out together?" Make it kind of a fun science challenge.

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    I'm with you bro, why the hell is water transparent? Why have I never asked that myself? Yeah OK light goes through but why? Commented Jul 15, 2015 at 15:08
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    I found it: physics.stackexchange.com/questions/105707/why-is-water-clear Commented Jul 15, 2015 at 15:11
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    I just looked it up too! Short answer is, "Lots of things are transparent at particular wavelengths. Because we're surrounded by water, especially when we were evolving in the sea, our eyes evolved to be able to see in the specific wavelengths that water happens to be transparent to." Commented Jul 15, 2015 at 15:22
  • Awesome comment thread for this answer! One of my favourite quotes about science is that the three most important words are "I Don't Know" followed closely by "Let's Find Out!" This perfectly illustrates how taking this route leads to learning something extremely cool - and a whole raft of 'What If?' questions open up as a result!
    – Dave B
    Commented Jul 15, 2015 at 16:57
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    +1 @CaptainCodeman -- My answer would be: To Stack Exchange!
    – Josh
    Commented Jul 17, 2015 at 7:19

"Why" is a semi-specific invitation to interact and to teach

The child is saying, to paraphrase:

"Please talk to me about the water. In addition, please bring in other interesting topics related to the water which I may or may not be aware of yet. I am in a mood to learn. Also, I like it when you engage with me verbally because it makes me feel happy and loved. Please continue to do this."

But he has no words, so he says:

"Why is the water transparent?"

A good answer to this question might bring in a discussion of light from the sun, and how very very BIG the sun is. You might say how light is stopped by most things, but can pass through water. It might look at other things that are see though, like windows.

You might try colouring the water to change the light. You might hold paper behind the coloured water to make a pretty pattern. You might hold two glasses of different coloured water in front of each other to see the attenuation. You might try to make the water opaque by mixing cornflour with it.

You might then branch out and look at focussing light, perhaps use a magnifying glass to light a fire, look at how the fire makes light because the gas is hot and glowing. Talk about how the light from the fire can go through the water too, etc.


If you are uncertain whether a question is about the definition of a term, you can quickly figure it out by asking. In this case: "do you know what transparent means"?

If the answer is "no", you explain what transparent means. (This isn't a philosophical question in any deep sense; it's just a definition of a word. You needn't worry about whether your son is a foundationalist or a fallibilist or a coherentist or whatever; just tell him what people use words to mean.)

If the answer is "yes", or "you can see through it", or anything like that, then you can go on to explain what you can about the transparency of water (or explain that you actually aren't sure why, or that you do know reasons why but that they only make sense if you know many other things that you haven't taught him yet, or say you should go read about it on Wikipedia, or whatever).


I think it would be important to know what prompted the question. The way I would interpret it in the absence of further context would be your second option. Something like:

I can't see through rocks, nor trees, nor dogs, so what is it about water that makes it possible for me to look through it?


Children need short, concise answers that makes sense in the development of their understanding of the world. Speaking as a 'tempered' parent, I would simply answer, "because it doesn't have a colour, just like glass, or the air".

That should do the trick.

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    I don't agree that children need short, concise answers, but if I wrote an answer my first example would be the same as yours. I immediately thought to compare it to glass, and then the air in that order. However, I would expound upon it, and talk about how we can put things in water to make it change color. If you keep giving them information, they keep picking it up and they don't have an opportunity to ask "Why?" over and over ;)
    – user11394
    Commented Jul 15, 2015 at 23:54

I have a vague recollection of asking "how come?" "how?" and "what?" in rapid succession as a young child, when confronted with a new topic. These are among the (mostly) "w" words that are question words. So that child will want to know more about topics like "water" and "transparent." And he's also getting a good "workout" on the question words themselves.


I'd target an answer that's both accurate and appropriate to his level of understanding.

A water related counter-example - I heard a young boy ask his father why it rained. The father answered "because the plants need water to grow."

The guy failed on both points. The water cycle is pretty cool and not tough to explain to a child, as we've all seen puddles evaporate, and can launch from there into the process of cloud formation, etc.

His failure on accuracy really struck me. I couldn't tell if he was trying to go the 'God' route or was just struggling for what he thought was the simplest answer, but either way, he blew it in my opinion.

  • Technically that answer could also relate to the anthropic principle rather than 'God'.
    – Random832
    Commented Jul 19, 2015 at 11:35
  • Perhaps. But he could have stuck with accurate, and then offered the further reason. Commented Jul 19, 2015 at 12:32

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