There is a spectrum ranging from zero to total separation of language by person. Usually, a simultaneous bilingual child's situation is somewhere in the middle. Some linguistic experts, dating from the early 20th century, have maintained that the best way to facilitate bilingual acquisition is to have each main input carrier (usually parents) use one and only one language with the child. By having each parent speak one of the two languages, this method (known as the ) attempts to prevent the child from confusing the two languages.