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.


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.

  • 5
    I'm pretty sure that ''These series' value is unmatched'' is valid, if a little unwieldy. – HorusKol Jan 26 '11 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 '11 at 16:16
  • I missed an apostrophe in the last example, fixed. It should be there because it's plural. – user3444 Jan 27 '11 at 16:17
  • 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". – Bennett McElwee Nov 8 '15 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 '11 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 '11 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 '11 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. – Wolfpack'08 Jun 10 '15 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 '15 at 3:51

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