These rules, necessarily called morphological rules, concern the way structural units are organized in word forms.
Morphemes, as we have to bear in mind, have a considerably stable phonological structure. This also applies to the situations in which they serve as the base for any kind of productive rule application, such as inflectional or derivational affixation. (the form HELP, for instance, does not change its form on the occasion of changing the lexical category by adding a suffix such as –FUL, as in HELPFUL.)
Alternatively, morphemes may have varied form in particular contexts, when we speak of allomorphic variations of that morpheme. This is to say that the phonemic content of certain morphemes is not retained in all occurrences, but it undergoes a kind of alteration due to certain conditions in the immediate surrounding of this form. (For the sake of illustration, the form decide changes its phonological content into DECIS- when the adjective forming suffix –IVE is to be appended, so as to obtain the form decisive.)
These phonological variations in morphemes are rule governed and in order for us to be able to discuss the changes that occur not only in English, but in other languages, as well, we should introduce the terms MORPHOPHONEME and MORPHOPHONEMIC CHANGE.
MORPHOPHONEME is a term which belongs to the intersection of morphology and phonology. It is used to indicate a phoneme, or more specifically a phonological variant, usually found on the final parts of morphemes, which carries particular grammatical meaning. It is an abstract unit which has varied concrete realizations in language. The change in form of these in concrete realizations signals a difference in grammatical form, i.e. meaning. Thus, morphophonemic studies are used to express different grammatical categories.
This is a phenomenon which can be detected elsewhere. Is Serbian (Junak, Junače, Junaci)- the word final phoneme is realized in different phonological environments as /k/, /tς/ or /ts/, making thus formally the difference between nominative case singular, vocative singular and nominative plural.
MORPHOPHONEMIC RULES, or morphological changes, called SANDHI in more traditional terms, are changes which occur in the phonological content of morphemes so that they can adapt to different grammatical functions or categories. Furthermore, sometimes it is necessary for a root of a word to change so that we could obtain a different part of speech or grammatical form
Lexical and grammatical units that interact in lexical terms have mutual effect in processes of world building. At times it is the base that has a stronger influence than the affix, so that the affix undergoes a formal transformation.
Morphophonemic rules can affect either the base or the affix that is to be added.
MORPHOPHONEMIC RULES AFFECTING THE AFFIX
Assimilation is such a morphemic change in which the last consonant of the prefixal morpheme undergoes assimilation of sorts, changes into a phoneme identical with the starting phoneme of the word root. More or less, this is a case of loss of phonemes. This is called COMPLETE ASSIMILATION:
a) IN + LITERATE > ILLITERATE
b) IN + MORTAL > IMMORTAL
c) IN + REGULAR > IRREGULAR
This is most often caused by the tendency to facilitate the pronunciation of the two morphemes in the combination, by trying to use phonemes which are related or similar according to the criterion of the place of articulation. If the last prefixal phoneme changes completely and is identified with initial in the root, it practically merges with it and disappears in pronunciation.
There is also PARTIAL ASSIMILATION when the last prefixal phoneme is not completely merged, but changed into another from the set of phonemes articulated on the same place of articulation. Bilabial plosives have the greatest strength for assimilating other phonemes into bilabials.
EN + BELLISH > EMBELLISH
IN + BALANCE > IMBALANCE
IN + POSSIBLE > IMPOSSIBLE
A process quite opposite to assimilation, as the name itself indicates. With this stage, two phonemes form two different morphemes, most often the last of prefix and the first of the root are dissimilated in such a way that they are no longer the same phoneme, but the first one is changed into a different one. The reason for that is easier morpheme identification. The difference may be in the place of articulation, or another sound quality. This is not frequently present change.
IN + NOBLE = INNOBLE > IGNOBLE
IN + NOMINY = INNOMINY > IGNOMINY
This morphemic change is also known as palatalisation. It refers to the process of combining or fusing two different consonants into a single one, different from the other two. This common phenomenon occurs when two morphemes meet each other in derivative, and the final consonant of one, velar or alveolar by the place of formation, and the initial of the other, the sound /j/ most often, get combined into a palatal sound.
Voicing refers to the change of the phonemic content of the base when an affix is to be attached. The final consonant of the base is changed to match the consonant nature of the initial phoneme in the affix. This normally occurs when the noun plural suffix for regular plural formation is to be added to a nominal base. The voiced /z/ exerts a strong voicing influence on the final labiodental and interdental fricative consonants that end certain nouns. In this case, the voiceless consonants /f/ and /Θ/ assume the form of their voiced counterparts /v/ and /ð/.
Baths /ba: θs/ or /ba: ðs/ ; youth /ju: θs/ or /ju: ðs/
This morphemic rule does not apply consistently, as many exceptions would ascertain, such as chiefs, beliefs, etc., nor does it occur in similar morphological and phonological circumstances, such as the case of genitive case markation – wife’s, thief’s, etc.
LOSS OF THE PHONEMES
With this change on or more than one phoneme is dropped from the original morpheme and its phonological content is altered. When we say ‘original’, we mean the most usual allomorph of a particular morpheme, the ‘default allomorph’, so to speak.
As opposed to the previous one, this change involves adding another phoneme to the phonological content of the morpheme. This is not a very customary change in English, and usually occurs with so called ‘silent’ letters in writing which represent no phonemes in the root. This is to prove, once again that in morphology it is the phonemic content of morphemes that matters and not the orthographic one.
BOMB – BOMBASTIC; LONG – LONGER; SOLEMN – SOLEMNIZE;
SIMPLE CONSONANT CHANGE
Simple consonant change means that the last or final consonant in a morpheme undergoes a change of sorts when a suffix is to be added. This is quite frequent phenomenon in English, particularly when it comes to deriving adjectives from verbs.
DESPISE – DESPICABLE; ELECTRIC – ELECTRICITY; EXTINCT – EXTINGUISH;
Gradation is the complex change in the sense that it involves two processes occurring one after the other. It is the case that after adding certain derivational suffixes, the main stress of the word shifts from the first syllable onward and is observed on another syllable, usually the second. This actually brings about the weakening of the vowel in the first syllable, so that it reduces to a half sound of /ə/. Apparently, the syllabic vowel has changed in quality and we call this occurrence vowel change. Thus, gradation is a combining of shifting of the stress and changing of the vowel.
COURAGE – COURAGEOUS; INDUSTRY – INDUSTRIAL; PARENT – PARENTAL; SYMBOL – SYMBOLIC;
ABLAUT IN DERIVATION
Ablaut is a linguistic phenomenon also known as CHANGE OF SYLLABIC VOWEL or MUTATION. As the names of this morphemic change suggest, it refers to a kind of change in the syllabic vowel or a morpheme, or the vowel of a morpheme, or the vowel which bears the primary stress. It may occur in inflection, but it also appears with affixation, when the base alters its syllabic vowel after the addition of a suffix. This kind of regularity can be noticed with nominalization of simple adjectives.