71. In words ending with the s sound but with a final e, only s is added to form the plural, but in pronouncing the word we then have two syllables, thus:
| house | place | size | cage | niche |
| houses | places | sizes | cages | niches |
72. Letters, figures, signs, etc., are made plural by adding an apostrophe and the letter s ('s), thus:
- Cross your t's and dot your i's.
- Do you know the table of 4's?
While most of our nouns form their plural in this regular way by adding s or es, there are some nouns that form their plural by some other change in the form of the word.
73. Notice the following list of words and their plurals:
- fly
- flies
- city
- cities
- key
- keys
- day
- days
- story
- stories
- enemy
- enemies
- tray
- trays
- boy
- boys
These nouns all end in y, yet they form the plural differently. Some simply add s and the rest change the y to i and add es. Can you discover the reason?
Wherever the y is preceded by a vowel, as e in key, a in tray, o in boy, the plural is formed by adding s. But when the y is preceded by a consonant, as l in fly, r in story, t in city, and m in enemy, the y is changed to i and es added in forming the plural.
If the singular ends in y after a consonant, change y to i and add es in the plural.