3.2. The difference between allophones and phonemes.

Allophones of the same phoneme need the following requirements:

1. though they possess some similar features they may show difference.

2. They never occur in the same phonetic context.

The allophone which is heard in isolation or stands in the position where it is not the subject (in such words as door, dark, etc.) and doesn’t undergo any distinguishable changes in the chain of speech is called “principal”. The allophones which are influenced by the neighbouring sounds and change the articulation are called “subsidiary”.

The examples below illustrate the articulatory modifications of the phoneme [t] in various phonetic contexts:

[t] in "tea" is a bit palatalized; in "not there" it is dental; in "not quite" it loses its plosion; in "little" it is pronounced with the lateral plosion; in "not many" - with the nasal plosion; in "try" it becomes post-alveolar; in "stare" - non-aspirated. In spite of the differences in the pronunciation of [t] in different positions it can be easily noticed that all its allophones possess some common features, all of them are forelingual, fortis stops. The native speaker is aware of the phonemes of his language but much less aware of the allophones: he will not hear the difference between two allophones like the alveolar and dental consonants [d] in the words “wide” and “width”. The reason is that the phonemes have an important function in the language: they differentiate words like “tie” and “die” from each other. Allophones on the other hand have no such function, they usually occur in different positions in the word and hence, cannot be opposed to each other to make meaningful distinctions. Hence, the allophones of the phoneme do not obstruct the listener and the speaker to understand each other.

In linguistics function is generally understood as the role of the various elements of the language in distinguishing the meaning. The function of the phonemes is to distinguish the meaning of morphemes and words. The native speaker doesn’t notice the difference between the allophones of the same phoneme because this difference does not distinguish meanings.

3.3. Invariant of the phoneme.

But at the same time they realize, that allophones of each phoneme possess a bundle of distinctive features that makes the phoneme functionally different from all other phonemes of the language concerned. This functionally relevant bundle of articulatory features is called the invariant of the phoneme. None of the articulatory features that form the invariant of the phoneme can be changed without affecting the meaning. All the allophones of the phoneme [d] are occlusive, forelingual, lenis (if occlusive articulation is changed for constrictive one, [d] will be replaced by [z] – e.g. breed – breeze; [d] will be replaced by [g] if the forelingual articulation is replaced by the backlingual one: dear – gear; the lenis articulation of [d] cannot be substituted by the fortis one without changing the meaning: dry – try).