14 Types of Phonological Rules
In spoken language, one important pattern is how certain phones are pronounced differently, yet are treated as the same conceptual object by speakers. For example, consider the English words atom and atomic. In most varieties of North American English, the consonant phone in the middle of atom is pronounced as an alveolar flap; remember that the alveolar flap is symbolized in the IPA by [ɾ]. But in the word atomic, the corresponding phone is a voiceless alveolar stop followed by a notable puff of air, symbolized in the IPA as [tʰ], where the superscript [ʰ] represents the puff of air (called aspiration). However, these two words are clearly related: atomic is built from the word atom, both in pronunciation and in meaning. Because of this, it is convenient to think of these two sounds as being the same object on some abstract conceptual level, despite being physically different.
This object is called a phoneme, and its various physical realities as phones are called its allophones. We can think of a phoneme as a set of allophones, with each one connected to certain specific positions. So in this case, we might say that the set {[ɾ], [tʰ]} is a phoneme, with [ɾ] and [tʰ] each being allophones of that phoneme, used in different situations, called environments.
The most common types of environments require one or more specific phonetic properties immediately to the left, one or more specific phonetic properties immediately to the right, or a combination of both. As with most aspects of linguistics, the environments for allophones can be more complex than what is presented in the simpler cases discussed in this textbook.
By convention, phonemes are often notated with just a single symbol in slashes / /, because the number of allophones can get quite large, and it would be too cumbersome to continue listing out all of the allophones as a set. The choice of symbol depends on certain assumptions, but for now, we can represent this phoneme with /t/.
Both of these allophones of /t/ occur between two vowels or syllabic consonants, but the flap [ɾ] is followed by an unstressed vowel or syllabic consonant, while the aspirated [tʰ] is followed by a stressed vowel or syllabic consonant. So we might conjecture that stress is at least partially responsible for determining which allophone to use for /t/.
We can test that conjecture by looking at other words where this phoneme occurs (fortunately, it is often spelled with the letter <t> in English) and seeing which allophone is used. In [ˈmɛɾl̩] metal and [məˈtʰælək] metallic, we see the same pattern as in atom and atomic, so our conjecture holds. There are other pairs of related words that show the same pattern: [ˈbæɾl̩] battle and [bəˈtʰæljn̩] battalion, [ˈkrɪɾək] critic and [kraɪˈtʰiriə] criteria, etc.
If we look beyond related words, we see the same pattern. English words with /t/ between two vowels or syllabic consonants tend to have the flap [ɾ] if the second is unstressed but a