What is the correct singular and plural possessive forms of the word given Thomas a last name?

Answer 1

There are two accepted forms for possessive singularnouns that end with an s:

Add an apostrophe (') after the existing s at the end of the word:

• Thomas'

Add an apostrophe s ('s) after the existing s at the end of the word:

• Thomas's

Examples:

The meeting is being held in Mr. Thomas' office.

The meeting is being held in Mr. Thomas's office.

The plural form of the noun Thomas is Thomases.

The plural possessive form is Thomases'.

Example: The Thomases' house is number fourteen.

Answer 2

The correct singular possessive form is "Thomas's last name" for both singular and plural nouns.

Answer 3

With Thomas being a last name, the singular possessive would be Thomas's. The plural is Thomases. The plural possessive is Thomases'.