Pidgins and creoles are contact languages that develop when groups lack a common language. A pidgin is used for basic communication between adults with different first languages. If a pidgin becomes the primary language of children, it evolves into a creole with an expanded vocabulary and stable grammar rules. There are different theories on how creoles form, including that isolation leads children to "re-create" a new language from a pidgin. Creolization more readily occurs when groups have no access to the standardized language, such as slaves in the Americas.