Steven Strogatz on math, from basic to baffling. It’s
traditional to teach kids subtraction right after addition. That
makes sense — the same facts about numbers get used in both,
though in reverse. And the black art of “borrowing,” so crucial
to successful subtraction, is only a little more baroque than
that of “carrying,” its counterpart for addition. If you can
cope with calculating 23 + 9, you’ll be ready for 23 – 9 soon
enough. At a deeper level, however, subtraction raises a much
more disturbing issue, one that never arises with addition.
Subtraction can generate negative numbers. If I try to take 6
cookies away from you but you only have 2, I can’t do it —
except in my mind, where you now have negative 4 cookies,
whatever that means. Subtraction forces us to expand our
conception of what numbers are. Negative numbers are a lot more
abstract than positive numbers — you can’t see negative 4
cookies and certainly can’t eat them — but you can think about
them, and you have to, in all aspects of daily life,