Though phonological rules can be written in prose, they can also be written in rule notation. The use of rule notation is often more concise than the use of sentences. I will provide a few examples to illustrate.
In English and many other languages, a vowel is nasalized when it is followed by a nasal in the same syllable. This is the case with words such as "sand" and "camping." This rule can be expressed with the following rule notation:
V ---> [+nasal]/_ [+nasal]$
This rule states that a vowel is nasalized in the environment before a nasal in the same syllable.
Another rule of English is the nasal assimilation rule. This states that an alveolar nasal becomes a velar nasal before a velar plosive. This is the case with words such as "ink" and "singer." Here is the rule in rule notation:
[+alveolar][+nasal] --> [+velar]/_ [+velar][-continuant]
This rule states that an alveolar nasal becomes a velar nasal in the environment before a velar plosive.
The vowel lengthening rule of English is also easy to express in rule notation. This rule states that a word-final vowel becomes long as in "see" and "yellow." This is the rule in rule notation:
V --> [+long]/_#
This rule states that a vowel becomes long in the environment word-final.
English also has a rule which deletes laterals before bilabial nasals. This is the case in words such as "calm," "palm" and "salmon." This is not true in all cases. The word "helmet" does not follow this rule, but nevertheless it applies in many cases. This can thus be called a variable rule as opposed to a categorical rule. In rule notation, the rule can be expressed as follows:
[+lateral] --> 0/ _ [+bilabial][+nasal]
This rule states that a lateral is deleted before a bilabial nasal.
Aspiration is another well-known rule in English. This states that a voiceless plosive is aspirated before a stressed vowel. This is the case in words such as "take," "party," "cold," "please," "prince" and "appear." Here is the rule in rule notation:
[-voice][-sonorant][-continuant]--> [+SG]/ _ ([+sonorant])([-nasal])V [+stress]
This rule states that a voiceless plosive is aspirated in the environment before an optional liquid or glide and a stressed vowel.
Rule notation is common in phonology. It is used as an alternative to prose in the expression of phonological rules. The examples demonstate the use of rule notation to express common phonological rules of English.