"What do you mean?" asked Betty. "Well," said John slowly, "what if we make up a number, say 'i', so that i i = -1." "Can we do that?" queried Betty. "Why not!" declared John. "But there is no such number that has that size," said Betty. "I know," replied John, "but the idea can exist in our imagination!" quipped John. "I think we should call it an imaginary number."