In linguistics, cover symbols (sometimes informally called wildcards, analogous to wildcard characters in computing) are broad letters or symbols used to represent classes of sounds. Such systems are useful for describing sound changes in historical linguistics, phonotactics in phonology, and ambiguous or underspecified identification in phonetics.
The symbols below are defined for indeterminate sounds by the Extensions to the International Phonetic Alphabet (extIPA), which recommends the use of a surrounding circle . Note that these are all manners of articulation.
may also be used for any voiced sibilant. may be used for any implosive.
Several symbols are commonly used for indeterminate places of articulation.
may also be used for any voiceless alveolar, in which case is used for any voiced alveolar.
One may prefer to use iconographic hooks on for certain places.
Those reconstructing Proto-Indo-European phonology use the following cover symbols, some of which differ from the examples above.
Capitalized vowels are commonly used in discussions of languages with vowel harmony. They often indicate different harmonic variants of an underlying archiphonemic vowel.
In phonotactics, cover symbols for syllable structures are often written with Greek letters.