Linguistics refers to the study of language in humans and its relationships to history, society, and cognition. It is concerned with matters such as probing the nature of language structures as a communicative system, providing organized descriptions of languages, documenting how linguistic systems developed historically, and exploring the likelihood that there are universal language structures.
Cognitive linguistics views that the essence of language is inherently based in evolutionarily-developed faculties. The guiding principle is that the creation, learning, and use of language should be explained by general reference to human cognition.
This branch of linguistics studies the effect of aspects of society, which include expectations, context, and cultural norms, on the usage of language. It is also concerned with the differences in dialects between groups that are separated by some social variables, such as religion, ethnicity, level of education, gender, status, etc.
Sociolinguistics is also concerned with how creation and adherence to social rules is used to group individuals in socio-economic classes or social class. Since people use language differently from place to place, its usage differs among social classes. It is these sociolects that this branch of linguistics studies.
This school of thought uses the concept of generative grammar, which is a finite set of rules that you can apply to produce sentences, which are grammatical in a specific language, and no others.
In the 1960s, the branch of psycholinguistics developed rapidly as an initiative towards cognitive psychology and adopted theories in generative linguistics. However, as both psycholinguistics and cognitive psychology have matured, generative linguistics has become of less use.
Also known as diachronic linguistics, historical linguistics studies language change. Its major concerns are to account and describe observed changes in certain languages and describe speech community history. It also aims at reconstructing the pre-history of languages, determining their relatedness, and grouping them into families of languages. Historical linguistics is also concerned with developing general theories about the hows and whys of language changes.
Traditionally dominated by the fields of second language acquisition and language education, this branch of linguistics is concerned with using theories in linguistics to address real-world problems. In the 1990s, researchers employed research methods used cognitive psychology. Today, applied linguistics is a cross-disciplinary mix of linguistics, education, anthropology, and psychology.