suppose you have two bags, one bag holding five apples and a second bag holding three apples. grabbing a third, empty bag, move all the apples from the first and second bags into the third bag. the third bag now holds eight apples. this illustrates the combination of three apples and five apples is eight apples; or more generally: "three plus five is eight" or "three plus five equals eight" or "eight is the sum of three and five". numbers are abstract, and the addition of a group of three things to a group of five things will yield a group of eight things. addition is a regrouping: two sets of objects that were counted separately are put into a single group and counted together: the count of the new group is the "sum" of the separate counts of the two original groups.