When it comes to Irregular Plural Forms the best piece of advice is to learn them as if they are totally new words. That is, don’t consider them as exceptions to a rule or even a rule in themselves; consider them as new vocabulary, new words, new lexical items.
Out of curiosity, there you go some of the main patterns (rules) of irregular plural forms in the English Language. If you are interested in learning more about the regular plural forms, just click here.
1. Some words (nouns) that end in ‘-f‘ or ‘-fe‘ change ‘-f‘ or ‘-fe‘ to ‘-ves‘:
- wife > wives
- knife > knives
- wolf > wolves
- self > selves
- leaf > leaves
- thief > thieves
- hoof > hooves
2. Some words change the vowel sound in their plural forms:
- man > men
- woman > women
- goose > geese
- foot > feet
- tooth > teeth
- louse > lice
- mouse > mice
3. Some words still have their plural form as it was in Old English:
- child > children
- ox > oxen
Nouns that end with ‘o‘ are really tricky sometimes. We can postulate rules, but they are so confusing to learners of English that they are not going to be mentioned here. There are also the cases of English words which come from other languages (borrowed words), especially from Latin or Greek. It’s not possible to mention all of them here.
Thus, keep in mind that the real best way to learn the plural forms of English nouns is to have a very good dictionary at hand. So, when in doubt, look up the word in the dictionary to check its plural form.
For example, say that you are not sure about the plural form of “photo“. Then, you go to Meriam-Webster Online Dictionary and type the word there. When you get the result for your search, you get the following information:
- Main Entry: pho·to
- Pronunciation: \ˈfō-(ˌ)tō\
- Function: noun
- Inflected Form(s): plural photos
Notice that you have the plural form of the word in there. In my opinion, it’s way better to check a dictionary than trying to memorize rules and their exceptions.