“What’s the sofa for?”

That’s the question I ask my grade-school son when I see him walking or jumping on the sofa. That may seem an odd parenting choice, but there’s a big reason I do it, and it has to do with Aristotle.

Professor Michael Sandel asks a provocative question: if the finest Stradivarius violin in the world is up for auction, and two people are bidding for it, who would it more justly go to: the richest person in the world, who wants to put it on display, or the best violinist in the world, who wants to play it?

I’d guess most people would say that the richest person should get it if they offer the most money. And people are probably right that the law should let the violin go to who pays the most, and not try to meddle in who deserves it based on merit, or based on how they’re planning to use it. But that doesn’t tell us whether it’s right morally for things to turn out that way.

If you disagree, consider: What if the richest person wanted to buy the violin not in order to display it, but in order to publicly burn it? Doesn’t that just seem wrong?

There are different ways we can get at that moral question, some of them looking for a rule or principle against destroying things, and others imagining how people would miss out on beautiful music if a great violin were destroyed. But Aristotle gives a third approach that I happen to love: asking what a violin is for. It is for making music, and surely the best thing that can happen is for a wonderful musician to use it for its purpose.

This principle has lots of uses. Facebook is a great tool when it is for keeping up with friends and family, and a lousy tool for trying to change other people’s minds about political issues. Science is a wonderful tool for understanding how the world works, but deficient if it’s expected to explain the meaning of life.

Or with parenting: when teaching young adults about sex, you can gives rules because “God says so” or warn against STDs or pregnancy. But consider the power of also talking about what sex is for, and teaching your teens to behave accordingly. Or if you’re explaining to your kids why they need to do school, you could tell them “that’s what we do in our family,” or that it will help them get a job. But consider the power of telling them that they have a purpose as well, that they are for something, and that education will help them grow into strong, knowledgeable, good, and Godly people–so they can live out all the parts of whatever their purpose turns out to be.

I will admit the sofa example is silly. I want my son to see that the purpose of the sofa is for sitting on, but of course a sofa can be for somersaults and playing at times as well.

But my real goal is to prime my kids to see the world in a certain way, that asking what something is for is one great piece of making good decisions.