Morph, Morpheme & Allomorph 

Morph, Morpheme and Allomorph are the units of a Language that are studied under Morphology, a branch of linguistics.

Morphology is the field of linguistics focused on the study of the forms and the formation of words in a language including their inflection, derivation and composition. It is the study of the smallest grammatical unit of a language. These basic elements are technically known as morphemes.

Let's now discuss what a Morpheme is:

Morpheme :

Morpheme is the smallest indivisible unit having meaningful content and grammatical function.

According to George Yule-

a morpheme is a minimal unit of meaning or grammatical function.

"a morpheme is the smallest contrastive unit of grammar".

for example, the word book and pen both are the smallest units and are contrastive that means they are not the same or identical. Smallest means they can not be further subdivided, if we divide them further they will result into meaningless remainders. 

A Morpheme is not identical to a word. Morpheme may or may not stand alone whereas a word can stand alone. Every word will comprise of one or two morphemes. 

For example the word dog has one Morpheme and when we add a plural marker -s to the word dog it becomes Dogs with two morphemes {dog,-s} where the suffix -S plays a grammatical function.

Morpheme can be defined as a word or part of a word that has a semantic content and that contains no other smaller part with a semantic content. For example, the word unforgivable has three morphemes {un} is a prefix meaning 'not' + {forgive} is the root Morpheme + {able} is an adjective forming suffix.

Morphemes are further divided into Free Morphemes, Bound Morpheme and Zero Morphemes. Let's discuss them one by one in detail:

1) Free Morpheme :

These morphemes can stand alone and work independently. They can function independently as words (e.g. town, dog, car, tree) and can appear within lexemes (e.g. townhall, doghouse).

2) Bound Morphemes:

Those morphemes which cannot stand alone and work independently. They occur only in combination with other morphemes or root word. For example: -un, -s, -er, -tion, -ly etc.

When added to the root word they start functioning: friend+ly --> friendly; un+educated --> uneducated.

Bound morphemes are further sub-divided as shown in the diagram. We will primarily focus on affixes that too mainly prefix and suffix.

(i) Affixes:

Affixes are always bound morphemes that are attached to a word. Affixes in a word are assigned for the grammatical function. Affixes are added to a word or a root of a word to change the meaning. 

Affixes can be further Classified onto various types based on the position they occur in a word such as prefix, suffix, circumfix and infix. We will only discuss prefix and suffix:

a) Prefix:

A prefix is the letter or a group of letters that is always placed at the beginning of a word. It always precedes the base word. 

For example, when un precedes necessary it forms un-necessary, il precedes logical and forms illogical, re precedes start and forms re-start.

b) Suffixes:

It follows the base. Suffixes are placed at the end of a word. for example: Cleanli-ness, regular-ly, avail-able etc.

Another classification of Bound morphemes is done into- derivational morphemes and inflectional morphemes.

(i) Derivational morphemes: 

Derivational morphemes are those which change the part of speech or meaning when combined with a root. Generally the affixes used with the root word are Derivational morphemes.

For ex. Verb to noun: sing --> singer,

Adjective to adverb : happy --> happily.

(ii) Inflectional morphemes:

Inflectional morphemes are those morphemes that do not change part of speech or meaning. It indicates the Syntactic or semantic relation between different words in a sentence.

For ex. Wait to waited, dog to dogs, play to playing.

3) Zero Morpheme :

Zero morphemes are those morphemes that are physically not present in a word, yet fulfil the grammatical requirement of the language. In the zero morphins the Null morpheme (no morpheme is added) is added to the root therefore it has a function but no form. 

For example- the verb put has same form in both past and present. 

Similarly the word cut has same form in both past and present. In the word sheep, the plural form is also Sheep.

Now, as we have discussed in detail about the morpheme and its various types, let's move towards Allomorphs and morphs.

Morphs:

A morph is the physical form through which a morpheme is represented. It is the physical form representation of a morpheme in a language. It is the recurrent distinctive sound or sequence of sounds. 

For example, the word people has two morphemes one is people (in singular form) but the other is its plural morpheme, but both these morphemes are physically represented in form of /people/. Hence the word people has two morphemes but one morph.

In another example the word 'no', there is no distinction between the morpheme and the morph as there is only one meaning associated with the pronunciation.

Allomorph:

They are the group of morphs that are the realisation of the same morpheme. Just as an allophone is the variation of a single phoneme, an allomorph is a variety of a single morpheme. 

For example: the English noun plural morpheme (s) has the following allomorphs -z as in dogs, -s in cats  and -iz as in buses.