It was once thought that learning two languages was detrimental to a child's cognitive abilities. This was due to the idea that the two languages were learned independently and the knowledge of learning one did not transfer into the other. It was thought that as more was learned in one language, less could be learned in the other. This gives the idea of there being a total amount of language acquisition, and so the pieces learned in each language together have to add up to this total. For this reason parents and teachers tried to force children to only learn one language instead of cultivating the ability to learn both.