Allophonic variation and phonetic context

The allophonic possibilities for a phoneme can depend on its position in relation to other phonemes. For example, the [n] in (nit, /n ih t/ needs to sound different from the [m] in (mit, /m ih t/, but the [n] in hand, /h ae n d/ does not need to contrast with [m] as there is no word /h ae m d/ that it could be confused with. It does need to be distinct from say [r], [sh] and [v] otherwise it could be confused with hard, hashed and halved. This shows that the [n] needs to still be a nasal in that it still needs to be identified with respect to some other consonants it doesn t need to be identified with respect to other nasals and so its distinctiveness with respect to [m] and [ng] need not be so precise as in other positions. As there are constraints on what phoneme sequences occur only distinctions between possible phonemes at a given point need to be maintained. The variability mainly arises from the fact that it is physically easier for a speaker to produce a given phoneme one way in one position and a slightly different way in a different position. 

It turns out that a great degree of verbal variability can be explained once we take phonetic context into accoimt. By this we mean that if we consider the identity of Ihe phonemes surroimd-ing the one we are interested in the identity of those surroimding phonemes helps explain why we see the variation in the speech. For example, we find in general that nasals before stops often share the place of articulation with the stop so we naturally get words such as hunt, / h ah n t/ and hump, / h ah m p/, where the [n] and [t] are both alveolar, and the [m] and [p] both bilabial but we don t get words /h ah m d/ and / h ah n p/, where the nasal has one place of articulation and the following stop has another. This phenomenon is called assimilation, reflecting the idea that the place of articulation of one phone assimilates to the other. 

Another common effect is called colouring, where the identity of the phoneme in question isn t affected or limited, but where the phoneme takes on some characteristics of the a neighbour- 

Basic phonetic context on its own is not enough to explain all the variation. Consider the behaviour of [t] in the words top, last and stop. In the first two, the [t] is normally aspirated, that is, there is a clear burst of energy after the release, which is heard of as a short section of noise. In stop there is no burst the vowel starts immediately after the release. This cannot be explained simply by context alone after all the [t] is aspirated when preeeded by a [s] is LAST and is also aspirated when followed by a vowel in top. These and other examples require reference to other structural factors such as the position in the syllable and word. 

As has already been mentioned, phonemes do not represent a single point in phonetic space if they did then each phoneme would have a unique acoustic pattern and file 

Basic phonetic context on its own is not enongh to explain all the variation. Consider the behaviour of [t] in the words top, last and stop. In the first two, the [t] is normally 

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