Theoretical Linguistics

Theoretical linguistics is the branch of linguistics which inquires into the nature of language itself and seeks to answer fundamental questions as to what language is; how does it work; how does universal grammar (UG) as a domain-specific mental organ operate; what are its unique properties; how does language relate to other cognitive processes, etc. Theoretical linguists are most concerned with constructing models of linguistic knowledge, and ultimately developing a linguistic theory.

The fields that are generally considered the core of theoretical linguistics are phonology, morphology, syntax, and semantics. Although phonetics often guides phonology, it is often excluded from the purview of theoretical linguistics, along with sociolinguistics. Theoretical linguistics also involves the search for an explanation of linguistic universals, that is, properties that all, or many languages have in common.

Phonetics is the study of speech sounds with concentration on three main points :

According to this definition, phonetics can also be called linguistic analysis of human speech at the surface level. That is one obvious difference from phonology, which concerns the structure and organisation of speech sounds in natural languages, and furthermore has a theoretical and abstract nature. One example can be made to illustrate this distinction: In English, the suffix -s can represent either /s/, /z/, or can be silent (written Ø) depending on context.

The field of articulatory phonetics is a subfield of phonetics. In studying articulation, phoneticians attempt to document how humans produce speech sounds (vowels and consonants). That is, articulatory phoneticians are interested in how the different structures of the vocal tract, called the articulators (tongue, lips, jaw, palate, teeth etc.), interact to create the specific sounds.

...
Wikipedia