Two terms are (often loosely) used to refer to linguistic disciplines studying that part of the linguistic sign which de Saussure called the acoustic image: phonetics and phonology
The importance of sounds as vehicles of meaning is something people have been aware of for thousands of years. However, systematic studies on the speech sounds only appeared with the development of modern sciences. The term phonetics used in
connection with such studies comes from Greek and its origins can be traced back to the verb phnein, to speak, in its turn related to phn, sound. The end of the 18th century witnessed a revival of the interest in the studying of the sounds of various languages and the introduction of the term phonology. The latter comes to be, however, distinguished from the former only more than a century later with the development of structuralism which emphasizes the essential contrastive role of classes of sounds which are labeled phonemes.
The terms continue to be used, however, indiscriminately until the prestige of
phonology as a distinct discipline is finally established in the first half of the 20
th century. Though there is no universally accepted point of view about a clear-cut border line between the respective domains of phonetics and phonology as, indeed, we cannot talk about a phonological system ignoring the phonetic aspects it involves and, on the other hand, any phonetic approach should take into account the phonological system that is represented by any language, most linguists will agree about some fundamental distinctions between the two.
