Why do you add es to words that end in ch to make them plural?

In the English language, plural Words DO NOT always end with an "s" or "es" suffix, since foreign Words are often borrowed permanently in English

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Alumni, alumnae, dice [di is an alternate plural], curricula, deer, cattle, fish, geese, stadia, teeth, feet, these, those, them, you and we are examples of common Words which end in letters other than "s" or "es". Some of the Words have retained their original Latin plural letters and some are merely exceptions to the "s" and "es" rule to which you refer.

The following entry from AOL's Homework Help :

You already know how to make most nouns into plurals just by adding an -s at the end of the Word. There are plenty of Words that do not follow the rule, however.

Here is an easy case to remember: If a Word ended in -s, -z, -x, -sh, or -ch, add -es to the end.

Examples: dress - dresses; fizz - fizzes; fox - foxes; wish - wishes; watch - watches.

When a noun ends in -o, you also have to add -es.

Examples: hero - heroes; tomato - tomatoes

Exceptions to the rule: studio, piano, kangaroo, zoo, buffalo, cargo, motto, . Just add -s to these Words.

If a noun ends in a consonant plus the letter "y", change the "y" to "i" and add -es.

Examples: city - cities; country - countries

When a noun ends in -f or -fe, you change the "f" to "v" and add -es.

Examples: knife - knives; half - halves; scarf - scarves

Here is one that always gave me trouble. I hope this makes it easier for you!

Sometimes a singular noun ends in -um or -on. To make it a plural, change the -um to an -a.

Examples: curriculum - curricula; phenomenon - phenomena

How about nouns that end in -ex or -ix? To make them plural, change that ending to -ices.

Examples: vertex - vertices; index - indices

Nouns that end in -us become plurals by changing the ending to -i.

Example: stimulus - stimuli

Some nouns are always plural, but do not end in "s".

Examples: cattle, police, people.

Read an English grammar textbook and/or a dictionary to learn more about plural Word endings.

P.S. Thanks to AOL for their Excellent explanation!

An oddball plural : one die, two or more dice. One mouse, two mice. One goose, two geese. One tableau, two tableaux. BUT -- One moose, two moose. One deer, two deer.

More InformationEnglish is generally considered to be one of the most 'irregular' of common languages. That means that it's difficult to learn because there are so few structural rules, and because the few that exist are broken constantly in unpredictable ways.

(Examples of more 'regular' languages include Latin and any of the Romance languages -- French, Spanish, Italian and Portuguese.) (Even less 'regular' examples abound, such as Mandarin Chinese and Navajo.)

This irregularity in language stems largely from the mixed heritage of the original English, and continues to the present day with the incorporation of the influences of large bodies of immigrants to the UK and especially to the US, a nation of relatively short heritage, but long diversity.

More information

There are also plurals derived from Old English, namely ox, oxen and child, children. Brethren is also such a plural although the singular form of "brether", a Word form of brother, has disappeared, as well as undergoing a change in meaning.