Every human language may be described as a system at each of the four levels of linguistic description, namely morphology, phonology, syntax and semantics. At each of these levels, a linguistic system comprises a number of sub-system which make up its structure. Thus, a language may also be described as a system of system. At the level of phonetics and phonolog, a language selects, from a general pool of speech sounds, a finite number of vocal sounds which are combined and used for it’s Communicatative and other purposes.
Looking at human vocal organs, out appears that their primary functions are biological. Even though they are also used for breathing, chewing, cutting, swallowing and smelling, they have been adapted for the production of the speech sound of any human language. But human languages are different in terms of their sound inventories. The point is, each language has its own number of sounds which are combined in a number of indefinite patterns according to its own phonological rules. This is what make each language unique as systematic patterns of structure, and perhaps why English uses forty-four sound segments, French forty, Italian twenty-seven, Yoruba twenty-seven and Hawaiian only thirteen.
There are four basic approaches to the study of speech sounds. These are articulatory, acoustic, auditory and forensic. Articulatory phonetics studies how speech sounds are made or articulated. Acoustic phonetics studies the physical properties of speech as sound waves in air. Auditory or perceptual phonetics studies the perception of speech sounds via the ears. The forensic phonetics studies speech sounds in the form of recorded utterance used for identifying a particular speaker, especially in a legal case.
The articulatory approach help the user of English as a second language to understand how the sounds of English are articulated as well as their basic characteristics. This knowledge may help to improve their pronunciation competence or fluency in the actual use of the language. It may also improve the degree of intelligibility of their utterances and therefore their communicative competence.
According to Yule in his book introduction to language, phonology is concerned with the abstract or theoretical aspect of speech sounds while phonetics is concerned with their actual physical articulation. Thus, by studying the systems and patterns of speech sounds in a language, we are actually studying phonology. It is phonology that explains the underlying design, the blueprint of the sound type, which provides the basis for all the variation in different physical articulations of that sound type in different contexts.