Phonetics and phonology are branches of linguistics concerned with sounds (or the equivalent aspects of sign languages). Phonetics is largely concerned with the physical aspects of sounds such as their articulation, acoustics, production, and perception. Phonology is concerned with the linguistic abstractions and categorizations of sounds.

Linguists focusing on structure attempt to understand the rules regarding language use that native speakers know (not always consciously). All linguistic structures can be broken down into component parts that are combined according to (sub)conscious rules, over multiple levels of analysis. For instance, consider the structure of the word "tenth" on two different levels of analysis. On the level of internal word structure (known as morphology), the word "tenth" is made up of one linguistic form indicating a number and another form indicating ordinality. The rule governing the combination of these forms ensures that the ordinality marker "th" follows the number "ten." On the level of sound structure (known as phonology), structural analysis shows that the "n" sound in "tenth" is made differently from the "n" sound in "ten" spoken alone. Although most speakers of English are consciously aware of the rules governing internal structure of the word pieces of "tenth", they are less often aware of the rule governing its sound structure. Linguists focused on structure find and analyze rules such as these, which govern how native speakers use language.

Sub-fields that focus on a grammatical study of language include the following:

It is often believed that a speaker's capacity for language lies in the quantity of words stored in the lexicon. However, this is often considered a myth by linguists. The capacity for the use of language is considered by many linguists to lie primarily in the domain of grammar, and to be linked with competence, rather than with the growth of vocabulary. Even a very small lexicon is theoretically capable of producing an infinite number of sentences.

Über die Verschiedenheit des menschlichen Sprachbaues und ihren Einfluß auf die geistige Entwickelung des MenschengeschlechtsOn the Variety of the Structure of Human Language and its Influence upon the Mental Development of the Human Race

Sociolinguistics is the study of how language is shaped by social factors. This sub-discipline focuses on the synchronic approach of linguistics, and looks at how a language in general, or a set of languages, display variation and varieties at a given point in time. The study of language variation and the different varieties of language through dialects, registers, and idiolects can be tackled through a study of style, as well as through analysis of discourse. Sociolinguists research both style and discourse in language, as well as the theoretical factors that are at play between language and society.

Developmental linguistics is the study of the development of linguistic ability in individuals, particularly the acquisition of language in childhood. Some of the questions that developmental linguistics looks into is how children acquire different languages, how adults can acquire a second language, and what the process of language acquisition is.

Chaika (1990) showed that people with schizophrenia who display speech disorders like rhyming inappropriately have attentional dysfunction, as when a patient was shown a color chip and then asked to identify it, responded "looks like clay. Sounds like gray. Take you for a roll in the hay. Heyday, May Day." The color chip was actually clay-colored, so his first response was correct.'

Computational linguistics is the study of linguistic issues in a way that is "computationally responsible", i.e., taking careful note of computational consideration of algorithmic specification and computational complexity, so that the linguistic theories devised can be shown to exhibit certain desirable computational properties and their implementations. Computational linguists also work on computer language and software development.

Forensic linguistics is the application of linguistic analysis to forensics. Forensic analysis investigates the style, language, lexical use, and other linguistic and grammatical features used in the legal context to provide evidence in courts of law. Forensic linguists have also used their expertise in the framework of criminal cases.