To say that a language's phonology involves the deployment of that language's phonetic resources within the framework of its morphology and syntax is virtually tantamount to saying that a language's phonological system cannot be identified with either its phonetic or morphosyntactic system but rather mediates between those systems. This situation can be illustrated by a few English words: mopper, mop, slobber, pop. First, the plural suffix -s is pronounced differently in moppers and mops, like the z of booze in the former but like the s of moose in the latter. Moreover, these differences in pronunciation of the plural -s are not idiosyncratic facts about the words mopper and mop (as, for example, could be claimed for dice as the plural of die), but rather bespeak a pervasive regularity of English. The z pronunciation of -s is the norm for nouns ending in a voiced sound--that is, a sound articulated with concomitant vibration of the vocal cords (see PHONETICS). Similarly, the s pronunciation of -s is the norm for nouns ending in a voiceless sound--a sound made with the vocal cords at rest.
The preceding discussion might suggest that phonology is not necessary, and all that is needed is a correlation between the morphological fact that English has a morpheme, the plural suffix -s, and the phonetic facts that this morpheme has two pronunciations--z following voiced sounds and s following voiceless sounds. Exactly the same z-s pattern, however, is found in two other morphemes in addition to the noun plural -s: for the third-person-singular present-tense suffix -s (slobbers, like moppers; pops, like mops) and the possessive suffix -'s (the pronunciation of mopper's is identical to that of the plural moppers, and likewise the pronunciations of mop's and the plural mops are the same). Thus three morpheme-pronunciation statements now must be formulated--one for each of the three morphemes involved--even though ostensibly the same pattern is in some way involved for each of the three cases. It is in large part situations like these that have led linguists to posit the existence of a phonological level of language organization.
Rather than relating the three suffix morphemes of the previous paragraph directly to their pronunciations, they can be said to share an abstract phoneticlike symbolization--a phonological representation--which will arbitrarily be called X. Then one pronunciation statement can be formulated for X--a phonological rule--to the effect that X is pronounced as s following a voiceless sound, but as z following a voiced sound.
The manner in which phonological rules are formulated and the names and symbols used vary considerably from linguistic school to linguistic school and from theory to theory. The phonological element that serves as input to the rule, symbolized by X in the above example, is variably called a morphophoneme, underlying segment, or phoneme. Despite differences of other sorts, all theories of phonology recognize the importance of distinctiveness in the organization and function of sound systems, normally by taking phonemes to be distinct from one another, with non-phonemic differences in sound following from phonemic distinctions. Thus it usually assumed that mob and mop differ distinctively (phonemically) in the difference b = p, while the difference in vowel length follows from that (the pronunciation of o being longer before b than before p).
Segmental and Suprasegmental Phonology
Segmental phonology is the phonology of vowels and consonants; suprasegmental or prosodic phonology involves phenomena such as stress (intensity) and tone (pitch). An accentual pattern involves the deployment of suprasegmentals within a word (for example, the stress differences between the noun insert--with stress on the first syllable--and the verb insert--with stress on the second syllable--), whereas an intonational pattern involves suprasegmentals within the framework of a sentence (for example, all the words in Mary worries Martin are accentually stressed on the first syllable, but the stress in Martin is intonationally most prominent). Because the sentence characteristically constitutes the framework for intonation, and because sentences are fundamentally syntactic constructs, intonation is one phonological phenomenon whose domain goes beyond morphology.