In 1957 a piece of literature appeared that would come to affect how we view language, human behaviour and language learning. B.F Skinner's Verbal Behaviour (1957) applied a functional analysis approach to analyze language behaviour in terms of their natural occurrence in response to environmental circumstances and the effects they have on human interactions.^[3] Skinner's behaviour learning approach relies on the components of classical, which involves unconditioned and conditioned stimuli, and operant conditioning but particularly the elements of operational conditioning. Operational conditioning refers to a method of learning that occurs through rewards and punishments for behaviour. Behaviour operates on the environment to bring about favorable consequences or avoid adverse ones. These same ideas of operant conditioning can also be applied to language acquisition because Skinner believed that language could be treated like any other kind of cognitive behaviour. According to the behaviourist theory, language learning is a process of habit formation that involves a period of trial and error where the child tries and fails to use correct language until it succeeds. Infants also have human role models in their environment that provide the stimuli and rewards required for operant conditioning. For example, if a child starts babblings, which resembles appropriate words, then his or her babbling will be rewarded by a parent or loved one by positive reinforcement such as a smile or clap. Since the babblings were rewarded, this reward reinforces further articulations of the same sort into groupings of syllables and words in a similar situation (Demirezen, 1988).^[4] Children also utter words because they cause adults to give them the things they want and they will only be given what they want once the adult has trained or shaped the child through reinforcement and rewards speech close to that of adult speech. Before long children will take on the imitation or modeling component of Skinner's theory of language acquisition in which children learn to speak by copying the utterances heard around them and by having their responses strengthened by the repetitions, corrections and other reactions that adults provide. However, before a child can begin to speak, they first start by listening to the sounds in their environment for the first years of their life. Gradually, the child learns to associate certain sounds with certain situations such as the sound of endearment a mother produces when feeding her child. These sounds then become pleasurable for the child on their own without being accompanied by food and eventually the child will attempt to imitate these sounds to invite the attention of his mother or another adult. If these sounds resemble that of adult language the mother will respond with reward and the operant conditioning process begins.

Noam Chomsky's innateness or nativist theory proposes that children have an inborn or innate faculty for language acquisition that is biologically determined. According to Goodluck (1991), nativists view language as a fundamental part of the human genome, as a trait that makes humans human, and its acquisition is a natural part of maturation.^[5] It seems that the human species has evolved a brain whose neural circuits contain linguistic information at birth and this natural predisposition to learn language is triggered by hearing speech. The child's brain is then able to interpret what she or he hears according to the underlying principles or structures it already contains (Linden, 2007).^[6] Chomsky has determined that being biologically prepared to acquire language regardless of setting is due to the child's language acquisition device (LAD), which is used as a mechanism for working out the rules of language. Chomsky believed that all human languages share common principles, such as all languages have verbs and nouns, and it was the child's task to establish how the specific language she or he hears expresses these underlying principles. For example, the LAD already contains the concept of verb tense and so by listening to word forms such as "worked" or "played". The child will then form a hypothesis that the past tense of verbs are formed by adding the sound /d/,/t/ or /id/ to the base form. Yang (2006) also believes that children also initially possess, then subsequently develop, an innate understanding or hypothesis about grammar regardless of where they are raised.^[7] According to Chomsky, infants acquire grammar because it is a universal property of language, an inborn development, and has coined these fundamental grammatical ideas that all humans have as universal grammar (UG). Children under the age of three usually don't speak in full sentences and instead say things like "want cookie" but yet you would still not hear them say things like "want my" or "I cookie" because statements like this would break the syntactic structure of the phrase, a component of universal grammar. Another argument of the nativist or innate theory is that there is a critical period for language acquisition, which is a time frame during which environmental exposure is needed to stimulate an innate trait. Linguist Eric Lenneberg in 1964 postulated that the critical period of language acquisition ends around the age of 12 years. He believed that if no language was learned before then, it could never be learned in a normal and functional sense. It was termed the critical period hypothesis and since then there has been a few case examples of individuals being subject to such circumstances such as the girl known as Genie who was imposed to an abusive environment, which didn't allow her to develop language skills.