I'm looking at the financial definition of series: a group of stocks or options that have common characteristics. Source

How would I form the possessive and plural of this term? I'm guessing it is series' and series respectively.

Sample sentences, not sure of correctness:

He purchased one series.

He purchased multiple series.

This one series' characteristics are worth researching. <- This feels like it should be series's, but it looks so wrong.

These series' value is unmatched.

3 Answers 3


All correct but the last one.

If you are talking about one series:

This series' value is unmatched

If you are talking about multiple series:

These series' values are unmatched.

If you are talking about multiple series valued together:

The value of these series' is unmatched.

  • 6
    I'm pretty sure that ''These series' value is unmatched'' is valid, if a little unwieldy.
    – HorusKol
    Jan 26, 2011 at 22:15
  • Thanks! I was more concerned with the "series'" rather than "values is/are" but thanks for pointing that out too.
    – Marcin
    Jan 27, 2011 at 16:16
  • I missed an apostrophe in the last example, fixed. It should be there because it's plural.
    – user3444
    Jan 27, 2011 at 16:17
  • 2
    Is the apostrophe really necessary in the last example? I think when you are talking about an intrinsic quality you wouldn't normally use a possessive with of. For example, you would say "my aunt's pen" and "my aunt's age"; with of, you might say "The pen of my aunt's", but "the age of my aunt". Nov 8, 2015 at 22:41

I think I agree with HorusKol. It's not wrong to say These series' value is unmatched, just awkward.

Think of similar examples with other nouns whose plurals are identical to their singular forms:

This sheep's fleece is white

These sheep's fleeces are black

These sheep's field is enormous

You may choose to construct a periphrasis to avoid confusion (especially if the line is to be spoken rather than read), but it's not incorrect to use a concise form from which the context makes the meaning plain.

  • 1
    +1 particularly for 'choosing to avoid confusion', which is surely the aim.
    – CJM
    Jan 26, 2011 at 23:21
  • Isn't it rather rare for a word whose singular and plural forms are the same, to also end in an 's'? I can think of a few where singular ends in 's' but plural is completely different, such as "octopus". Yet I can't think of any other than this definition of "series" that don't change form when pluralized.
    – Marcin
    Jan 27, 2011 at 16:20
  • 1
    facies and species are two others that spring to mind, although I can't think of any that aren't direct borrowings from Latin like these three.
    – gpr
    Jan 27, 2011 at 22:27
  • I thought you put the apostrophe after words ending in s, like plural cases. Then you pronounce two 'es' sound when speaking them. The sheeps' wool = "the sheepses wool" = more than one sheep's wool. Another example: "my parent's" vs "my parents'". It removes the ambiguity. I would opt for sheep's in "these sheep's" for simplicity in reading and pronunciation, but certainly if I thought there would be ambiguity (i.e., "my sheep" or "the sheep"), I would opt for sheeps' to distill that. Of course, that's stylistic. Jun 10, 2015 at 16:19
  • I think that only works for proper names ending in S, e.g. James. It used to be the case that you should write "James'" and pronounce it "James". These days you would write and say "James's" and all of these are correct. But sheeps's is definitely incorrect, and you wouldn't pronounce it sheepses either. Unfortunately that does lead to ambiguity in some cases, so if it's not clear from context what you mean, I would change the sentence.
    – gpr
    Jun 30, 2015 at 3:51

This thread is ten years old, but I feel like I need to add a voice of reason here for anyone referring to this in the future.

In academic settings, I have always been taught, and have always followed (without ever being corrected), the following simple and (for the most part) unambiguous conventions for writing the possessive forms of nouns:

Three Rules for Writing ALL Possessive Nouns (Common and Proper):

All Singular Possessive Nouns:

1. [singular noun] + [apostrophe] + s

Plural Possessive Nouns:

2. [plural noun whose spelling ends in "s"] + [apostrophe]


3. [plural noun whose spelling does not end in "s"] + [apostrophe] + s


dog → dog's fur
bus → bus's engine
box → box's contents
witch → witch's broom
city → city's history
man → man's name
child → child's parents
this deer → this deer's antlers
cactus → cactus's spines
crisis → crisis's origins
this species → this species's evolution
this lens → this lens's curvature
this TV → this TV's resolution
my mother-in-law → my mother-in-law's opinion
a passerby → a passerby's attention
Canada → Canada's allies
the United States → The United States's role (see examples below)
the U.S. Constitution → The U.S. Constitution's detractors
the Bill of Rights → the Bill of Rights's authors
Michelle → Michelle's sister
James → James's house
Texas → Texas's capital
Descartes → Descartes's legacy
McDonald's (the restaurant) → McDonald's's offerings

dogs → dogs' owners
buses → buses' engines
boxes → boxes' contents
witches → witches' coven
cities → cities' similarities
men → men's names
children → children's parents
these deer → these deer's habitat
cactuses (or cacti) → cactuses' spines (or cacti's spines)
crises → crises' origins
these species → these species' divergence
these lenses → this lenses' curvatures
these TVs (or these TV's) → these TVs' prices (or these TV's' prices)
their mothers-in-law → their mothers-in-law's opinions
several passersby → several passersby's attention

Some real usage examples:

"The United States's Power Scares These Seven Countries, Which See It as a National Threat" (https://www.newsweek.com/usa-threat-countries-scared-645092)

"Can the United States’s global reputation be repaired?" (https://www.aljazeera.com/program/inside-story/2020/11/4/can-the-united-states-global-reputation-be-repaired)

"Due to the United States’s special international status" (https://www.brookings.edu/opinions/is-america-declining/)

  • 2
    There are differences of opinion about some of these cases and style guides differ about things like Jesus's/Jesus': grammarphobia.com/blog/2018/08/jesus-2.html
    – Stuart F
    Oct 30, 2021 at 11:41
  • I'd go further than Stuart. I'd say << the United States’s global ... >> say is far less common than << the United States’ global ... >> (and Google searches certainly back up this opinion). All this has been covered in other threads; the usual advice is "add 's if you'd pronounce the extra syllable". Thus The Browns' house; Charles's house, say. Oct 30, 2021 at 12:00

Not the answer you're looking for? Browse other questions tagged or ask your own question.