Many years ago a well-known Canadian linguist, Jim Cummins, had already sketched out two different ideas of bilingual learning. On one hand, he said, we have the idea of separate underlying proficiency. In this case we view the mind as if two languages were housed separately within it, in two separate watertight compartments with a limited storage capacity. The two languages seem to work against one another. When some new language is added to one side, this causes an imbalance on the other side, and therefore loss of some of the other language. If we accept this view, knowledge and skills cannot transfer from one language to the other – it is as if blowing into the L2 balloon will inflate the L2 balloon but not the L1 balloon, and viceversa.