Do you remember the basic rule of arithmetic that changing the order of the numbers we're adding doesn't change the sum?  It's one of the most basic and intuitive rules of arithmetics, it's called the **commutative law**.

A binary operation is considered commutative if you get the same result after swapping operands. Obviously, addition is a commutative operation:  _3 + 2 = 2 + 3_.

But is subtraction a commutative operation? Of course not: _2 - 3 ≠ 3 - 2_. In programming, this law applies in the same way as in arithmetic.

Moreover, most of the operations we face in real life aren't commutative. In conclusion, you should always pay attention to the order of things you're working with.
