the commutative property means that the order in which the numbers are added or multiplied doesnt matter. so: 4+5=9 5+4=9 4x5=20 5x4=20 but what happens when you do that with subtraction? 4-5= -1 5-4= 1 4/5=.8 5/4=1.25 you cant change the order of the numbers in subtraction and division.