Can you figure out this riddle?

[Some Guy]

1 explains 2,
2 explains 3,
3 explains both

What's the concept?
No, one thing explains the second thing, the second thing explains the third thing, but the third thing explains the first two.
Three is not the answer!

One thing explains the second,
the second thing explains the third,
but the third thing explains the first two.

 

[SilverStar]

What? 1 explains 2? How in the world do numbers talk? 2 explains 3 and 3 explains both? OH!!!!!!!!!!!

1 + 2 is 3. See? I forget what a concept is. Sorry ^_^

 

[SpongeBob]

how is the answer 3? yes 1 + 2 = 3. But how then does 2 explain 3?