Part of one's knowledge of a language is knowledge of the phonology or sound system of that language the inventory of phones, the phonetic segments that occur in the language, and the ways in which they pattern. it is this patterning that determines the inventory of phonemes the segments that differentiate words.
Phonetic segment are enclosed in square brackets, [ ], and phonemes between slashes, / /. when phones occur in complementary distribution, they are allophones predictable phonetic variants of phonemes. For example, in English, aspirated voiceless stops such as the initial sounds in the words pill, till, and kill are complementary distribution (never occur in the same phonological environment) as the unaspirated voiceless stops following the s /s/ in spill, still, and skill; thus the aspirated p, t and k ([ph], [th], [kh]) and the unaspirated [p], [t], and [k] are allophones of the phonemes /p/, /t/, and /k/, respectively. On the other hand, phones which occur in the same environment and which differentiate words, such as the [b] and [m] in beat [bit] and meat [mit] represent two distinct phonemes, /b/ and /m/.
Some phonemes may be allophones of more than one phoneme. there is no one-to-one correspondence between the phonemes of a language and their allophones. In English, for example, stressed vowels become unstressed according to regular rules and ultimately reduce to schwa [ə], which is an allophone of each English vowel.
Phonological segments phonemes and phones are composed of phonetic features such as voiced, nasal, labial, and continuant, whose presence or absence is indicated by + or - signs. they distinguish one segment from another. when a phonetic feature causes a word contrast, as nasal does in boat and moat, it is a distinctive feature, whereas [+- aspiration] is not.
When two words (different forms and different meanings) are distinguished by a single phone occurring in the same position, they constitute a minimal pair. Some pairs, such as boat and moat, contrast by means of a single distinctive feature, in this case, [+- nasal], where /b/ is [- nasal]. Other minimal pairs may show sounds contrasting in more than one feature, for example, dip versus sip, where /d/, a voiced alveolar stop, is [+ voiced, - continuant] and /s/, a voiceless alveolar fricative, is [- voiced, + continuant]. Minimal pairs and sets also occur in sign languages; signs may contrast by hand configuration, place of articulation, or movement.
Some sounds differ phonetically but are non-phonemic because they are in free variation, which means that either sound may occur in the identical environment without changing the meaning of the word. The glottal stop [ʔ] in English is in free variation with the [t] in words such as don't or bottle and is therefore not a phoneme in English.
Phonetic features which are predictable are non-distinctive and redundant. The nasality of vowels in English is a redundant feature since all vowels are nasalised before nasal consonants. One can thus predict the + or - value of this feature in vowels. A feature may therefore be distinctive in one class of sounds and non-distinctive in another. Nasality is distinctive foe English consonants, but non-distinctive and predictable for English vowels.
Phonetic feature which are non-distinctive in one language may be distinctive in another. Aspiration is distinctive in Thai and non-distinctive in English; both aspirated voiceless stops and unaspirated voiceless stops are phonemes in Thai.
The phonology of a language also includes constraints on the sequences of phonemes in the language, as exemplified by the fact that in English two stop consonants may not occur together at the beginning of a word; similarly, the final sound of the word sing, the velar nasal, never occurs word initially. These sequential constraints determine what are possible but non-occurring words in a language, and what phonetic strings are 'impossible' or 'illegal'. For example, blick [blɪk] is not now an English word but it could become one, whereas kbli [kbli] or ngos [ŋɒs] could not. These possible but non-occurring words constitute accidental gaps.
Words in some languages may also be phonemically distinguished by prosodic or suprasegmental features, such as pitch, stress, and segment duration or length. Languages in which syllables or words are contrasted by pitch are called tone languages. Intonation languages may use pitch variations to distinguish meanings of phrases and sentances.
In English, words and phrases may be differentiated by stress, as in the contrast between the noun pe`rvert in which the first syllable is stressed, and the verb perve`rt in which the final syllable is stressed. In the compound noun ho`tdog versus the adjective + noun phrase hot do`g, the former is stressed on hot, the latter on dog.
Vowel length and consonant length may be phonemic features. Both are contrastive in many dialect of English.
The relationship between the phonemic representation of words and sentences and the phonetic representation (the pronunciation of these words and sentences) is determined by general phonological rules.
Phonological rules in a grammar apply to phonetic strings and alter them in various ways to derive their phonetic pronunciation :
1. They may be assimilation rules that change feature values of segments, thus spreading phonetic properties. The rule that nasalises vowels in English before nasal consonants is such a rule.
2 They may be dissimilation rules that change feature values to make two phonemes in a string more dissimilar like the Latin liquid rule.
3. They may add non-distinctive features that are predictable from the context. The rule that aspirates voiceless stops at the beginning of words and syllables in English is such a rule, since aspiration is a non-phonemic, non-distinctive, and predictable redundant feature.
4. They may insert segments that are not present in the phonemic string. Insertion is also called epenthesis. The historical rule in Spanish that inserted an [e] before word-initial /s/ consonant clusters is an example of an addition or insertion rule.
5. They may delete phonemic segments in certain contexts. Contraction rules in English are deletion rules.
6. They may transpose or move segments in a streing. These metathesis rules occur in many languages, such as Hebrew. The rule in certain dialects of English that changes an /sk/ to [ks] in final position is also a metathesis rule.
Phonological rules often refer to entire classes of sounds rather than to individual sounds. These are natural classes, characterised by the phonetic properties of features that pertain to all the members of each class, such as voiced, or, using + and - signs, the class specified as [+ voiced]. A natural class can be defined by fewer features than required to distinguish a member of that class. Natural classes reflect the ways in which we articulate sounds, or, in some cases, the acoustic characteristic of sounds. The occurrence of such classes, therefore, does not have to be learned in the same way as groups of sounds that are not phonetically similar. Natural classes provide explanations for the occurrence of many phonological rules.
In the writing rules, linguists use formal notations, which often reveal linguistic generalisations of phonological process.
A morpheme may have different phonetic representations; these are determined by the morphophonemics and phonological rules of the language. Thus the regular plural morpheme is phonologically [z] or [s] or [əz], depending on the final phoneme of the noun to which it is attached.
There is a methodology that linguists can use to discover the phonemes of a language, which, includes looking for minimal pairs and complementary distribution. The allophone of a phoneme that results in the simplest statement of the rules of distribution is selected as the underlying phoneme from which the phonetic allophones are derived. The underlying phoneme is selected from the allophone of that phoneme which give the simplest statement of the rule distribution, and the other allophones are derived from it via phonological rules.
The phonological and morphophonemic rules in a language show that the phonemic shape of words or phrases is not identical with their phonetic form. The phonemes are not the actual phonetic sounds, but are abstract mental constructs that are realised as sounds by the operation of rules such as those described above. Non-one teaches us these rules. And yet all speakers of a language know the phonology of their language better than any linguist who tries to describe it. The linguist's job is to make explicit what we know unconsciously about the sound pattern of our language.
