1+1 = MORE (or LESS)

A math whiz encourages you to play with your numbers

- Eugenia Cheng

WHY DOES one plus one equal two?

One possible answer is "It just does!" That is really a variation on "Because I said so!"-an answer that has been frustrating children for generations.

It is quite right to feel frustrated by that idea. Math can seem like a world of rules you just have to follow, which makes it seem rigid and boring. Whereas my love of math is somewhat driven by my love of breaking rules, or at least pushing against them. Both of those impulses play an important role in advancing human understanding, and in particular mathematical understanding.

So rather than think about why one plus one is two, let's go a little further and question whether it's even true all the time.

Sometimes, one plus one can equal more than two. If you have enough cash on you to buy one cup of coffee, and your friend has enough to buy one, then together you still might have enough to buy three. Because if you have 1.5 or even 1.9 times the money needed for a cup of coffee, that still only gets you one cup on your own.

One plus one can also equal more than two because of reproduction: Say you put one rabbit and another rabbit together. You might well end up with a lot of rabbits.