Forming the Possessive of Words Ending in -s

Answering students’ questions…

“Apostrophe s” (’s) is used for several reasons in English, such as for the contracted form of is and has, and also for indicating possession (belonging to someone). In general, we add ’s to a singular noun and add  to a plural noun ending in -s. For example, we would say the student’s book (for one student) and the students’ classroom (for many students). But what happens when the singular noun ends in -s? The rules for this have gone back and forth, which makes it difficult for ELLs (English language learners) and native speakers alike. As an editor, I have to keep up with the current guidelines as set out by popular style guides such as the Chicago Manual of Style. I thought I’d share the most recent “rules” with you so you can pass them along to your students! If you disagree with any of these guidelines, please share your opinion in the comment section below—it’s always interesting to learn what different teachers think around the world!

General Rule:

Note: If the plural noun doesn’t end in -s, then simply add ’s to the word (e.g., the children’s classroom).

Rule for Singular Words Ending in -S:

According to the Chicago Manual of Style, 16th edition, the general rule for forming possessives also applies to words ending in -s (sections 7.15–7.18). This rule applies to both common nouns and proper nouns (including names ending in -s, -x, and -z), as well as letters and numbers. Here are a few more examples from the Chicago Manual of Style:

  • a bass’s stripes
  • Marx’s theories
  • Borges’s library
  • Berlioz’s works
  • FDR’s legacy
  • 1999’s heaviest snowstorm
  • the Lincolns’ marriage (plural – last name “Lincoln”)
  • the Williamses’ new house (plural – last name “Williams”)

The Chicago Manual of Style also explains that nowadays, unlike in previous years, words ending in unpronounced -s and proper classical names of two or more syllables that end in an eez sound also follow the same rules, as noted in the following examples:

  • Descartes’s three dreams
  • the Ganges’s source

Basically, this is great news for us all because the same rules apply to almost every situation and are therefore easier to remember. English learners are always relieved when there aren’t a lot of exceptions to a rule!

I hope this post will ease your students’ minds,



Leave a Comment ↓

  1. ESL Library Staff says:

    Apr 17, 2014 at 9:02 pm

    Very useful post, Tanya. I know I’ve bugged you about this before. So, it’s grammatically correct to add “-es” to a proper name when forming a possessive, like in “the Williamses’ new house” case, right? Is this because of pronunciation?

    • Tanya Trusler says:

      Apr 17, 2014 at 9:09 pm

      Thanks, Tara! Yes, we need to add “-es” to names that end in -s, -z, -x, -sh, or
      -ch. You’re correct that this reflects how we pronounce “s” after these sounds—we need to add another syllable in order to be able to pronounce two sibilant sounds back to back.

      Compare my last name, Trusler (which doesn’t end in those sounds), with the name “Martinez”, which ends in -z.
      – Tanya Trusler’s home (one person) / The Truslers’ home (my whole family)
      – Maria Martinez’s home (one person) / The Martinezes’ home (her whole family)

      Don’t forget that the plural proper noun will not always be possessive! Consider these examples:
      – Let’s invite the Truslers to the party.
      – Let’s invite the Martinezes to the party.

      You can tell it needs a possessive apostrophe or apostrophe “s” if it’s followed by another noun (“home” in the above examples) and means “belonging to someone” (i.e., the Martinezes own the home, so it’s “the Martinezes’ home”).

      Hope that helps! :)

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