RULES FOR PLURAL IN ENGLISH (FROM WIKI PEDIA)
Regular plurals
The plural morpheme in English is suffixed to the end of most nouns. Regular English plurals fall into three classes, depending upon the sound that ends the singular form:
Where a singular noun ends in a sibilant sound—/s/, /z/, /ʃ/, /ʒ/, /tʃ/,or /dʒ/—the plural is formed by adding /ɨz/.
/s/ is 's' as in 'see'.
/z/ is 'z' as in 'zoo'.
/ʃ/ is 'sh' as in 'she'.
/ʒ/ is 'ge' as in 'beige'.
/tʃ/ is 'ch' as in 'cheese'.
/dʒ/ is 'j' as in 'jam'.
The spelling adds -es, or -s if the singular already ends in -e:
kiss kisses /ˈkɪsɨz/
phase phases /ˈfeɪzɨz/
dish dishes /ˈdɪʃɨz/
massage massages /məˈsɑːʒɨz/ or /ˈmæsɑːʒɨz/
witch witches /ˈwɪtʃɨz/
judge judges /ˈdʒʌdʒɨz/
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When the singular form ends in a voiceless consonant (other than a sibilant) — /p/, /t/, /k/, /f/ or /θ/, — the plural is formed by adding /s/.
/θ/ is the 'th' sound.
The spelling adds -s.
Examples:
lap laps /læps/
cat cats /kæts/
clock clocks /klɒks/
cough coughs /kɒfs/
death deaths /dɛθs/
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For all other words (i.e. words ending in vowels or voiced non-sibilants) the regular plural adds /z/, represented orthographically by -s:
boy boys /bɔɪz/
girl girls /ɡɜrlz/
chair chairs /tʃɛərz/
Morphophonetically, these rules are sufficient to describe most English plurals. However, there are several complications introduced in spelling.
The -oes rule: most nouns ending in o preceded by a consonant also form their plurals by adding -es (pronounced /z/):
hero heroes
potato potatoes
volcano volcanoes or volcanos
The -ies rule: nouns ending in a y preceded by a consonant usually drop the y and add -ies (pronounced /iz/). This is taught to many North American and British students with the mnemonic: "Change the y to i and add es":
cherry cherries
lady ladies
However, proper nouns (particularly those for people or places) ending in a y preceded by a consonant form their plurals regularly [1][2]:
Germany Germanys (as in The two Germanys were unified in 1990; this rule is commonly not adhered to as several book titles show,[3][4]; Sicilies and Scillies, rather than Sicilys and Scillys, are the standard plurals of Sicily and Scilly.)
Harry Harrys (as in There are three Harrys in our office)
The rule does not apply to words that are merely capitalized common nouns:
P&O Ferries (from ferry)
Other exceptions include lay-bys and stand-bys.
Words ending in a y preceded by a vowel form their plurals regularly:
day days
monkey monkeys
(Money/Monies is an exception, but money can also form its plural regularly.
