1090: Allophones (Definition) Dec 2, 2017

There are certain pairs of phonemes (sounds) that—in very specific contexts—would probably be indistinguishable in English, such as [p] or [b] in 'spot' (or 'sbot'). Nevertheless, the phoneme [p] can represent the sound produced by 'p' in 'pot', 'spot', and 'stop', even though they are all slightly different. While [b] and [p] may not be distinguishable in a few words, there are occasions when the difference changes the meaning, such as 'bin' and 'pin'. However, none of those different words before that have a sound represented by 'p' will change or lose meaning (in English) if one is used instead of the other. These are called 'allophones', because they all act as the same sound, in that one can be substituted for the other to an odd-sounding effect but identical meaning. In other words, these allophones are not part of a language's phoneme inventory. 

Another criteria for allophones, however, is that if one sound consistently assimilates to another in some given context, it is an allophone. Therefore, even though the sound [t͡ʃ] (like the CH in 'church') can create different meaning when it replaces [t] such as in 'porch' and 'port', because a T [t] before an R [ɹ] becomes a [t͡ʃ] (consider 'tap' [tap] and 'trap' [t͡ʃɹap]) [t͡ʃ] is considered an allophone of [t]. It should be noted that allophones change from language to language. There will be more on this tomorrow, considering other languages.