English consonantal allophones

While the physical difference between t and th in English is just as real as the difference between t and d, there is a fundamental linguistic difference between these two relationships. The selection of t versus d may constitute the sole difference between many different words in English: such words, where two words are differentiated exclusively by a choice between one of two segments, are referred to as minimal pairs.

The difference between [t] and [d] is contrastive (also termed distinctive) in English, since this difference – voicing – forms the sole basis for distinguishing different words (and thus, [t] and [d] contrast).

The choice of a voiceless aspirated stop such as [th ] versus a voiceless unaspirated stop such as [t], on the other hand, never defines the sole basis for differentiating words in English. The occurrence of [t] versus [th ] (also [k] versus [kh ], and [p] versus [ph ]) follows a rule that aspirated stops are used in one phonological context, and unaspirated stops are used in all other contexts. In English, [t] and [th ] are predictable variants of a single abstract segment, a phoneme, which we represent as /t/. Purely predictable variants are termed allophones – the sounds are in complementary distribution because the context where one variant appears is the complement of the context where the other sound appears. As we have emphasized, one concern of phonology is determining valid relations between pronounced segments and the abstract mental constructs that they derive from, the phonemes, which represent the unity behind observed [t] and [th ] etc. The implicit claim is that despite there being actual differences, [t] and [th ] (also [k] and [kh ], [p] and [ph ]) are in a fundamental sense “the same thing.” We reduce the output sounds [t th k kh p ph ] to just the set of sounds /t k p/, and a rule provides the information “realized as [t] vs. [th ]” to account for these regularities.