Pluralization is the process of inflecting a singular noun by adding affixes or changing certain letters in the singular noun form to give the plural form.

The plural form of many nouns in English can be formed as follows.

1. Add "s" to the singular form to form the plural. Example: dog -> dogs.
2. Add "es" for singular nouns ending in a sibilant sound. Example: dress -> dresses.
3. Change the terminal "y" to "i" and then add "es" when the singular noun ends in "y" not preceded by a vowel (or is not a proper name). Example: spy -> spies.

Unfortunately there are many English nouns whose plurals do not follow the rules above. A description may be found in Damien Conway's paper at An Algorithmic Approach to English Pluralization . MorphAdorner implements Conway's pluralization procedure for nouns. MorphAdorner always produces non-classical plurals.

You can try MorphAdorner's English noun pluralizer online.