Phonology is a branch of linguistics concerned with the sounds in languages.
What's a phoneme?
Phonemes are the individual sounds of a language. This is not the same as the spelling of a language (which is the orthography). Phonemes are represented by the International Phonetic Alphabet (IPA), which is used to transcribe the exact pronunciation of words in all languages worldwide. IPA even accounts for regional accents. Linguists use forward slashes to represent the IPA pronunciation of a word: bat /bæt/.
Here are the IPA symbols for English consonants and vowels:
Word stress in IPA is indicated with a ˈ before the stressed syllable: linGUIStics /lɪŋˈɡwɪstɪks/. Longer words may have secondary stress which is indicated by the ˌ symbol: proNUNciAtion /prəˌnʌnsɪˈeɪʃən/.
Vowel lengthening
A longer vowel is represented by the ː symbol. The word bead has a longer vowel sound than bid:
bead /biːd/ (long vowel)
vs.
bid /bɪd/ (short vowel)
Languages can have a short and long version of the exact same vowel. For instance in English the /i/ in city /ˈsɪti/ is not lengthened, but we do not think of this as a different vowel from its lengthened form illustrated above in bead /biːd/. Some languages, however, have short and long versions of the same vowel that make a meaningful difference. This is evident when two words differ by only one phoneme and have two different meanings. Linguists call these minimal pairs. In Australian English the words bid /bɪd/ and beard /bɪːd/ are minimal pairs differing only by vowel lengthening. Thus, in Australian English, we would say that /ɪ/ and /ɪː/ are two different phonemes.
In many dialects of English (American included) there is a no meaningful difference between the sounds /i/ and /iː/ (in that we do not find them as minimal pairs). Instead /i/ and /iː/ are analysed as one phoneme changing in different environments. Linguists call this phenomenon allophony; two allophones ([i] and [iː]) of the one phoneme (/i/). The principle of allophony does not just apply to vowel lengthening, but we will return to it later.
Other languages that make a meaningful difference between vowel lengths include Arabic, Japanese, Hebrew, Finnish and Hungarian.
Nasal vowels
Nasal vowels are, as the name suggests, vowels with a nasaly sound. They are best illustrated by the nasal sound quality in the words "huh?" and "uh-huh". Physiologically they are produced when air is allowed to escape through the nose as the vowel is being said. Any phoneme can be nasalised, however nasalisation is more common for vowels. Nasalisation is represented with a tilde: ã ẽ ĩ õ, etc.
Like vowel lengthening, some languages may make a meaningful difference between nasal and non-nasal vowels. French is one such language, where the words beau /bo/ ‘beautiful’ and bon /bõ/ ‘good’ differ by only nasalisation. In English, nasal vowels occur as allophones before nasal consonants (that is, consonants /n/, /m/ and /ŋ/, which are also produced by allowing air to escape the nose).
Other symbols
Other symbols for adding extra information to the sound quality of phonemes can be found here. Most of these symbols are not often used unless linguists are concerned with being overly precise with documenting the phonology.
Phonological rules
All languages have sounds that change slightly (or sometimes dramatically) based on the effects of other phonemes around it. These are known as phonological processes. We express them in writing as phonological rules. In technical terms, it is a way of expressing when and where a phoneme changes into one of its allophones.
There are a few examples in English. My favourite is probably the writer/rider example. Note that the words writer and rider are identical in pronunciation, despite different spelling, different meaning, and despite the fact that they come from two obviously different root words: write and ride. The consonant in the middle of the words writer and rider is neither a /t/ or /d/, but a quick tap of the tongue behind the teeth. Linguists call this a tap, and its IPA symbol is /ɾ/. It turns out the tap occurs consistently in certain environments. It occurs between the words litre and leader, and cider and sighter. If a pattern like this can be established it can said to be a phonological rule: /t/ and /d/ turn into a tap in between two vowels. The notation looks like this
t → ɾ / V_V
d → ɾ / V_V
where → means 'turns into', / means 'in the environment of' and V mean any vowel. We can package the two rules into one:
{t,d} → ɾ / V_V
When a word goes through a phonological rule such as this one we can give it a "narrow" pronunciation in square brackets:
writer /ˈɹaɪtə/ [ˈɹaɪɾə]
rider /ˈɹaɪdə/ [ˈɹaɪɾə]
The "broad" pronunciation (between forward slashes) can be thought of as the abstract pronunciation of the word; it is what we think the pronunciation is until we consciously analyse it and ties back to the meaning of the word (including its root word) and perhaps to the spelling of the word too. Meanwhile the narrow pronunciation is what the mouth and tongue are actually doing.
Another English phonological rule is vowel nasalisation. The rule is: vowels turn into nasal vowels before nasal consonants. Example: sing /sɪŋ/ [sɪ̃ŋ]. Formally it is written
V → V[+nasal] / _N
where N means nasal consonant, and square brackets [+nasal] to can be used to add a property to a class of phonemes.
Phonological rules have implications for how words will change pronunciation based on what affixes get attached. For example, imagine in your constructed language you make up a rule that o → u / _C (/o/ turns into [u] before any consonant). Now imagine you decided the way to form past-tense verbs is to add a suffix -t to the end of verbs, and the way to form present-tense is to add nothing to the verb. Now imagine your word for want is rito /ˈrito/. Your phonological rule will affect the root word in the past-tense only:
Present-tense: rito /ˈrito/
Past-tense: rito + t /ˈritot/ [ˈritut]
Types of Consonants
Consonants are phonemes that are articulated with complete or partial closure of the vocal tract. They contrast with vowels, which are articulated with the vocal tract relatively open.
Consonants can be broken down into classes based on a matrix of 1) where in the mouth the tongue is placed to article the sound (place of articulation) and 2) how the sound is articulated from that place (manner of articulation). You can see this on the standard IPA chart.
Manners of articulation
Stops
Stops are probably the most common type of consonants. Examples in English are p, b, t, d, k, g, where the air-flow through the mouth is momentarily completely blocked, and then released. We can contrast stops with consonants that have a continuous air flow, like s, z, m and n.
"Stop" describes a manner of articulation. Manners of articulation can be performed at various different places in the mouth (place of articulation). Note that the only difference between /p/ and /t/ is that in /p/ the air flow is stopped at the momentary closure of the lips, and in /t/ the air flow is stopped with the tongue behind the teeth. Both have the same manner of articulation, but the palce of articulation is different. There are other stops in the International Phonetic Alphabet that do not occur in English. For instance, Arabic has the stop whose place of articulation is way in the back of the throat, at the uvula. Its symbol is /q/ and might sound a little bit like an English "k" to untrained ears.
In phonological rule notation a capital S may be used to mean all stop consonants. Example: a > e /_S (/a/ turns into /e/ before any stop).
Nasal consonants
Nasal consonants are produced by allowing air to escape through the nose. In English they are /n/, /m/ and /ŋ/. In phonological rule notation a capital N may be used to mean all nasal consonants.
Fricatives
Fricatives are produced by forcing air through a narrow channel in the vocal tract, to create turbulent airflow. In English these include /s/, /z/, /f/, /v/, as well as /ʃ/ the sounded represented by ‘sh’, /ʒ/ as in pleasure, /θ/ as in thin and /ð/ as in this. In phonological rules they may be represented as F.
Affricates
Affricates are a combination of a stop and fricative in short succession. The best example in English is the ‘ch’ sound, which is actually a combination of a /t/ and a /ʃ/, resulting in /tʃ/.
Flap or tap
Flaps or taps are similar to stops but more brief. An example is /ɾ/ in rider.
Trills
Trills are produced with the tongue vibrating against some part of the mouth. A Spanish ‘r’ is a classic example of a trill, however they do not occur in most dialects of English.
Approximants
Approximants in English include /w/ as in water, /j/ as in you, and /ɹ/ as in ready. They are defined as phonemes where the vocal tract narrows at some place of articulation, enough to not be a vowel but not enough to create turbulent airflow such as a fricative. In phonological rules they may be represented as A.
Laterals
Laterals are various L-like consonants. In English the only lateral is /l/, but a few other types exist. In phonological rules they may be represented as L.
Places of articulation
Bilabial
Bilabial means ‘two lipped’ in Latin. These are consonants that are produced by closing lips together is some way or another. In English they include stops /p/ and /b/, and the nasal /m/. In phonological rules they may be represented as P.
Labio-dental
Labio-dental consonants are with the upper teeth touching the lower lip. In English they include /f/ and /v/.
Dentals and alveolars
Dental consonants are articulated with the tongue against the upper teeth, consonants such as /t/, /d/, /n/, /s/, /z/, and /l/. However in some languages "dentals" are actually produced slightly further back in mouth at the alveolar ridge. For this reason linguists may choose to represent dentals with diacritic symbols (t̪ d̪ n̪ s̪ z̪) to disambiguate them from the alveolar location. English only has alveolar consonants.
Dental consonants are sometimes further broken down into interdental, where the tongue is between upper and lower teeth: the ‘th’ sounds in English are interdental, /θ/ as in thin and /ð/ as in this.
Postalveolar
Postalveolar consonants are articulated with the tongue slightly further behind where alveolar consonants are produced. These include /ʃ/ ‘sh’, /ʒ/ as in pleasure, as well as affricates /tʃ/ and /dʒ/.
Palatal
Palatal consonants are articulated with the tongue against the middle part of the roof of the mouth (hard palate). In English the only palatal consonant is /j/ as in you.
Velar
Velar consonants are articulated with the back part of the tongue against the back part of the roof of the mouth (soft palate). In English these are /k/, /g/ and /ŋ/ as in ‘ng’ sounds. In phonological rules they may be represented as K.
Voicing
Voicing is best illustrated by the difference between phonemes /s/ and /z/. These two phonemes have the exact same manner and place of articulation; both fricatives in the alveolar position. So how do they differ? In producing these sounds you will notice your vocal chords vibrating during the articulation of the /z/. The term "voicing" refers to whether the vocal chords vibrate during the production of a phoneme. All phonemes have a voiced and voiceless counterpart, although not all of them maybe the present in a given language. They may be represented in phonological rules as C[+voice] and C[-voice]. The following tables shows voiced/voiceless pairs in English:
