Today my daughter asked me what a calorie is. I told her it was a unit of energy. Then she asked me what a unit is. I told her a unit is a single thing. And she asked, “But what IS it?” I was stumped. So, I did what any parent would in this day and age, I looked it up on my phone. This is what I found, “An individual thing or person regarded as single and complete but which can also form an individual component of a larger or more complex whole.” Let’s just say that did no good at all. I noticed another definition which seemed more apt to the original question, so I tried, “A quantity chosen as a standard in terms of which other quantities may be expressed.” That was even less successful than the first definition. I tried listing different types of units: an inch is a unit of length, a pound is a unit of weight, etc. That didn’t help much either.
I never did explain it in a way that satisfied her. (Although I think she does get what a calorie is.) Now I can’t help but wonder if I know what a unit is. How can I claim to know something if I can’t pass that knowledge along to someone else? It’s not like a unit is some amorphous thing like pornography. According to the dictionary definition, it is an actual thing. But it’s not a thing I can point at.
The more I’ve thought about it, the less satisfying the dictionary definitions are to me. I don’t know if it’s a case of looking at the same thing for too long makes it blurry, but now these definitions sound like gobbledygook. An individual thing that can form an individual component? A quantity that expresses a quantity? It’s not as bad as the definitions that use the word in the definition, “A unit is any thing that can act as a unit,” but it’s not much better.
I know I’ve spent way too much time thinking about this. I’m sure my daughter has already forgotten about it. But I’m going to be bothered until I can come up with a way to explain a unit that a kid can understand. I need to find something that I can point to and say, “That. That right there. That’s a unit.” Until then, I can’t help but think I simply don’t know the answer.