PHONEMICS
Phonetics describes the observable and concrete aspects of language (i.e., speech or sounds). There are other abstract and mental aspects of language that are not the subject of phonetics. We plan speech and then speak these plans. When we speak our planned speech, some changes take place due to biological and physiological constraints.
Phonetics can only describe the end result of our plans—speech. It does not describe the changes that occur to our plans; neither does it tell us what goes on in the human brain during the planning of speech. For instance, we all know that /ʃænbe/ is the correct form of the word meaning Saturday in Persian, yet we all pronounce it, unconsciously of course, as /ʃæmbe/. This shows that what we actually speak differs from what we plan to speak. In other words, speech planning and speech execution are somewhat different stories. That branch of phonology that is concerned with the explanation of these differences is called phonemics. As such, phonetics and phonemics are the two sides of a coin called phonology. Like phonetics, phonemics, too, is of two types: traditional and modern (or systematic). In traditional phonemics, abbreviations like the ones used in broad and narrow transcriptions were used. In modern phonemics, phonetic features are used.
Phonemics is the study of the system that governs the sounds of a language. Phonemics can also interact with morphology to bring about what is known as morphophonemics. We all know, for example, that the plural ending "s" is used in English to pluralize nouns. We also know that this ending can be pronounced in three different ways: /z/ in dogs, /s/ in books, and /əz/ or /ɪz/ in busses (usually called the allomorphs of the plural morpheme). This means that the same morpheme (i.e., the plural morpheme) has three surface realizations whereas it has only one mental or abstract realization. That is, in our mental dictionary (or our lexicon), there is only one entry for the plural morpheme; however, in actual speech, we pronounce this single morpheme in three different ways. This is because the surrounding sounds affect the surface realization of this morpheme in speech. Morphophonemics describes the mental processes that bring about such changes in the pronunciation of morphemes.
Phonemics accounts for at least two types of knowledge the speakers of a language possess: (a) the knowledge of sequential/phonological constraints, and (b) the knowledge of phonological processes. Phonological/sequential constraints refer to those aspects of human linguistic knowledge that explain why certain sound combinations are possible while certain other sound combinations impossible. Phonological processes explain the rules that account for the differences that exist between planned speech (i.e., phonemic representation of speech) and executed speech (i.e., phonetic representation of speech).
