The process of acquiring and developing language is a complicated one and there is no set explanation on how it happens. However, a number of theories have been developed over the years. Each theory has both strengths and limitations, which suggests that they may each explain a part of the language development process and should be viewed as a collective whole.
A popular theory on language development that is somewhat outdated today, but nonetheless was held to be true by many researchers, is the behaviourist theory, developed by B. F. Skinner. This theory states that the learning of all skills is based on responses to positive and negative reinforcement. It also assumes that language develops in the same way all other skills do. When a child is hungry and learns that saying the name of a food produces that food, he will then learn to use that name regularly. In certain situations, the behaviourist theory may be applicable, though it raises questions and concerns as a general theory of language development, including how it applies to internal thoughts and dialogue.
The innateness, or nativist, theory was created by Noam Chomsky and remains a popular theory in language development and acquisition. It states that all humans are born with a language acquisition device. These LADs contain the basic grammatical rules and knowledge common to all languages and allow children to understand the basic grammatical structures of languages they come into contact with, thus enabling them to develop those languages over time. This theory has been reworked over time and is supported by the finding of areas of the brain specifically relating to language functions.
The interactionist theory states that there is a both a biological and a social aspect to language development. It states that language is developed through a child's desire to communicate his or her thoughts and feelings. It includes the term scaffolding, which is when an adult alters his or her speech and uses baby talk when speaking to a child, which is usually a simplified version of language that allows a child to develop language skills more easily. However, since there are cultures that do not employ such talk and still have children acquiring languages, there are limits to this theory.
The cognitive theory of language development, by Jean Piaget, states that language skills are built in accordance with mental or cognitive development in a child. For example, there is a certain point in a child's life where he or she will be able to arrange objects by size. The cognitive theory posits that before this period in brain development, a child will not be able to use language that implies a relation to size, such as bigger or smaller. Some studies have found that certain aspects of language, such as the use of syntax, does not rely on intellectual growth, which means this theory does not apply generally, though perhaps is applicable in situations like the example given.