Why are they called numerators and denominators?

I’ve been doing fractions for several decades, and only yesterday did I find out how the numerator (the number on the top) and the denominator (the one on the bottom) got their names. I’m not sure that knowing why they’re called what they’re called will help too many folks who struggle with fractions, but I’m pretty sure it will help a few, so here goes.

The denominator tells you how big the piece is. So if the fraction is 4/5, the denominator tells you that a whole has been divided into 5 parts. Denominator is a fancy Latin-based way of saying “the namer.” If it helps, note the nom in the middle of the word. That’s the important part, and it looks a little like name.

The numerator tells you how many of those pieces there are. So in the 4/5 example, you have 4 of those 5 parts. If the denominator is the namer of the fraction, the numerator is the numberer. Now if that isn’t awkward, I don’t know what is. Especially because the roots you have to pay attention to all start with n, end with m, and have some vowel in the middle.

So it becomes easy to see that math can be as much an exercise in managing language as reading or writing. In Malcolm Gladwell’s book Outliers, he quotes a psychologist who has studied differences in math learning across cultures who explains that the Chinese for 3/5 is “out of five parts, three.” Makes the whole numerator/denominator scene a little easier to make sense of. Or at least it might if you learned it that way when you were young…

Click here for my review of Outliers.

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