The reasoning all relates to Einsteins theory of relativity. When an apple falls on your head and your like "Where did this come from?" well the answer to this question is that 2 plus 2 equals 4 not 5. If the answer were to be 5 in this problem it would have been orange not an apple. Now subtraction is a complety different concept. You see if you did 4 minus 2 wich we all know is 2 you would fall on the apple not the apple falling on you. Now here is a good way to explain multiplaction: when luke skywalker and the members of the rockaholics get in a fight luke would whop them to the ground. So whe you are defeated by a train jedi your dumbness would multiply by 6 billion putting you back on level 22 on runescape. Now when you divide it is like beating world of warcraft on super mega ultra geek squad difficulty. Its so hard no one can do that.

In our number system, which is basically the Arabic number system, which may have originally come from India, we give values to how many of something there is. It could be apples, oranges, computers, iphones, chairs, books, anything... We have a way of counting them. Some early cultures that didn't have this may have recognized one of something, two of something, or many of something. They may have had no understanding of two apples and two apples is four apples, they just knew about many apples and didn't think about adding, subtracting, or any other math. To them A bird in the hand really was better than two (or more) in the bush. It's all they understood. Some animals are like that.

Back to 2+2=4 (or 5). It doesn't matter what we call 2+2. They are just symbols that represent values and people long ago defined these symbols to mean these values and everybody else accepted them to mean these values. Arithmetic also has various rules that make the number system consistent so that it makes sense.

We defined the meaning of the numbers we use as 0 1 2 3 4 5 6 7 8 9, and a bunch of rules about getting bigger number values like 204, 75134 and even 4.7*10^52.

We all know that 1+1=2, because that's how we define "2"

similarly 1+1+1=3 (so does 2+1 and 1+2),

and 1+1+1+1=4 (so does 3+1, 1+3, 2+2)

and so on.

There is a whole lot of number fact and theory about the system and why it works.

If 2+2 were 5, than so would 3+1=5 and 1+1+1+1=5.

But than what would be 1+1+1+1+1? we would have to call it something else. Maybe use "4" since it wasn't being used for anything else. It would work just fine as long as everybody knew the new rules.

But they don't, so we are stuck with 2+2=4.

which is just fine because if we used 2+2=5, someone might go to answers.com and ask "Why is 2+2 5 and not 4?"