As we know, nouns can be countable and uncountable. Countable nouns are the ones that we can count and can be in plural form when they are more than one in quantity.
The canonical form of making the plural forms of nouns is adding the suffix -s to the end of a countable noun. There are also some other ways of making the plural forms of nouns in the English language that every learner of English must know in order to make the correct plural forms of nouns.
In learning the spelling and pronunciation of the plural forms of nouns it is recommended to learn the other rules first of all than adding only -s.
We have to add the letters -es to the base if the singular forms of nouns end in -s, -sh, -ch and -x as in the examples matches, buses, bushes, boxes.
Some grammar books say that the nouns ending in letter -o also take the suffix -es to make their plural. But this rule is not general. There are only a few examples for this rule: tomatoes, heroes, potatoes. On the contrary, most of the nouns that end in -o take the suffix -s to make their plural. For example photos, discos, kilos, pianos, studios, radios, studios, zoos and etc.
So, the rule, where it is said that «nouns ending in -o take -es to make their plurals» can be considered as an exception to the rule where it is said that «nouns ending in -o take only one-letter suffix -s to make their plurals.»
But there are also some nouns that end in -o and make their plural forms in two ways for the same noun by adding -s or -es: mango — mangos or mangoes, mosquito — mosquitos or mosquitoes, zero — zeros or zeroes, buffalo — buffalos or buffaloes.
In addition to the rules given above, there is a clear explanation to decide how to differ nouns ending in -o to add -s or -es. The following nouns do not have e in the spelling:
a) nouns ending in the singular in -o preceded by a vowel letter or a vowel sound: bamboos, embryos, kangaroos;
b) abbreviations such as kilos (kilograms), memos (memoranda), photos (photographs);
c) musical terms of Italian origin: concertos, contraltos, pianos, solos, sopranos;
d) proper names: Eskimos, Filipinos;
There is also some confusion in making the plural forms of the nouns ending in -y. But this rule can easily be explained by a simple rule which says that the nouns ending in «-y preceded by by a consonant letter» make their plurals by changing the y to i and then adding the two-letter suffix -es: country — countries, fly — flies, penny — pennies, story — stories, baby — babies, city — cities. This rule sometimes explained as omitting the letter y preceded by a consonant and adding -ies. This version is usually preferable to make the rule easier to understand.
Other nouns that end in the letter y for example «y preceded by a vowel letter» make their plurals simply by adding the suffix -s: boys, days, journeys, chimneys, cowboys, donkeys, trolleys, toys, keys and etc.
In the rules given above the learners of English may not pay attention to some common words such as «preceded by a consonant», «most of the nouns ending in -o» or «only a few nouns ending in -o» and others. This lack of attention leads to some confusion in learning to make the plural forms of the nouns.
Another rule with confusion is connected with the nouns ending in -f or -fe. If a noun ends in -f, we have to change f to v and then add -es: half — halves, shelf — shelves, leaf — leaves, loaf — loaves, thief — thieves, wolf — wolves. The same rule applies to the nouns ending in -fe: knife — knives, life — lives, wife — wives.
But some nouns that end in -f, just take the suffix -s to form their plurals: chef — chefs, chief — chiefs, cliff — cliffs, roof — roofs, sheriff — sheriffs, handkerchief — handkerchiefs.
But there are also some nouns that end in -f and make their plural forms in two ways for the same noun by adding -s or -es: dwarf — dwarfs or dwarves, hoof — hoofs or hooves, scarf — scarfs or scarves.
Some nouns don’t add -s or -es. Their old plural forms have survived in modern English: child — children, foot — feet, man — men, woman — women.
Several nouns borrowed from Latin, Greek and French are usually used in scientific context: radius — radii, stimulus — stimuli, genus — genera, amoeba — amoebae, antenna — antennae, formula — formulae, nebula — nebulae, analysis — analyses, appendix — appendices, index — indices, matrix — matrices.
The canonical form of the pronunciation of the plural forms of nouns is [s]. But there are also some specific cases which depends on the other sounds.
Syllable [iz] is added to any base ending in a sibilant in singular form if we make the plural form of these nouns: face [feis] — faces [feisiz], page [peidʒ] — pages [peidʒiz], match [mᴂtʃ] — matches [mᴂtʃiz], bus [bʌs] — buses [bʌsiz].
Voiced [z] without a vowel sound is added to any base ending in any voiced sound except a sibilant: boy [bᴐi] — boys [bᴐiz], friend [frend] — friends [frendz], motel [mǝutel] — motels [mǝutelz].
Voiceless [s] without a vowel sound is added to any base ending in any voiceless sound except a sibilant: desk [desk] — desks [desks], jeep [dʒi:p] — jeep [dʒi:ps].
In conclusion, I want to say that we have to learn spelling and pronunciation rules carefully and pay special attention to all the rules as learners of the English language.
- Raymond Murphy, English Grammar in use. Aself-study reference and practice book for intermediate students. Cambridge University Press.
- John Eastwood, Oxford Practice Grammar. Intermediate. Oxford University Press.
- R. A. Close. A Reference Grammar for Students of English. Moscow. Prosveshcheniye 1979.
- Fakhriddin Rakhmatov (compiled by), English Grammar in Practice. A self-study refence and practice book for intermediate and upper-intermediate Uzbek-speaking students of English. 2016.
- Anne Seaton, Y. H. Mew. Basic English Grammar for English language learners. Book 1. Saddleback Educational Publishing, 2007.
- Howard Sargeant. Basic English Grammar for English language learners. Book 2. Saddleback Educational Publishing, 2007.
 Sibilant sounds are [s], [z], [ʃ], [ʒ].