Universal Grammar: a Theory
In 1957, Noam Chomsky’s book Syntactic Structures came out; in this book, Chomsky (who has come to be considered a father of modern linguistics) elaborated on the idea of universal grammar.
What is universal grammar all about? It basically suggests that there is "an innate set of linguistic principles shared by all humans," an inbuilt grammar that we are all born already possessing.
The idea of universal grammar has been greatly disputed over the decades. Are we really hard-wired with language before birth, or is it developed as a result of the conditioning we receive after we are born? It is true that all languages and their grammar have many points of similarity worldwide; but is this due to our "innate set of linguistic principles shared by all humans" or is this rather due to the constraints of communication that result in all languages being similar?
Chomsky’s idea of universal grammar would answer that question by saying that because the human brain is hardwired with a limited set of rules for forming a language, thus all the languages of the world have similarities based on having a similar underlying structure.
Stratificational Linguistics, or Cognitive Linguistics: a Theory
Sydney Lamb was the chief proponent of a theoretical approach called stratificational linguistics (also known as cognitive linguistics).
As the adjective "stratificational" would suggest, this theory proposes that, in Lamb’s words, "A language may be regarded as a system of relationships. As such, it is not directly observable. The linguist can only observe the manifestations of linguistic structure, i.e., samples of speech and/or writing, and the situations in which they occur." The layers, or strata, of a language have their own rules of syntax and are all related to the other layers of language.
Behind Lamb’s linguistic theory was the idea that linguistic data was not something directly observable, or explainable. It could only be understood as the outworkings of complex neurological relationships and layers that could not be directly observed.
Two processes that receive a lot of focus in this theory are the processes of encoding and decoding. These processes are essentially used to describe what happens in communication between two individuals. There are ideas in the brain of one individual, which he, the speaker, encodes into language (or verbal cues); these ideas are then decoded by the brain of the one who hears what is being spoken. Thus, through a process of encoding and decoding, communication is achieved.
Functional Discourse Grammar: a Theory
Functional Discourse Grammar, originally proposed by Simon C. Dik, proposes that utterances are made up of four components: the conceptual component (which concerns the communicative intent of one who will make the utterance), the grammatical component (which includes the structuring and encoding of the communicative intent), the contextual component (which includes all the historical, cultural and other implications that will affect the utterance), and the output component (which is the realization of the utterance–whether in spoken word or writing).
Linguistic Theories: in Summary
In summary, these and many other second language acquisition linguistic theories attempt to explain the rationale behind the structure of human language, on a universal level. Why, and how, do we formulate and use language? These are deep questions that have been, and will continue to be, answered by linguists of the past, present and future.