Not nesseceraly:
Singular nouns ending with an "s" or "z" sound
This subsection deals with singular nouns pronounced with a sibilant sound at the end: /s/ or /z/. The spelling of these ends with -s, -se, -z, -ze, or -ce.
Traditionally it was more common to require and many respected sources
still do require that practically all singular nouns, including those
ending with a sibilant sound, have possessive forms with an extra s after the apostrophe. Examples include the Modern Language Association, The Elements of Style, and The Economist.[4] Such sources would demand possessive singulars like these: Senator Jones's umbrella; Mephistopheles's cat. Some respected style guides such as the Chicago Manual of Style recommend the more modern addition of an s but specifically state that both habits are correct.[5] Rules that modify or extend this principle have included the following:
- If the singular possessive is difficult or awkward to pronounce with an added sibilant, do not add an extra s; these exceptions are supported by The Guardian,[6] Emory University's writing center,[7] and The American Heritage Book of English Usage.[8] Such sources permit possessive singulars like these: Socrates' later suggestion; James's house, or James' house, depending on which pronunciation is intended.
- Classical, biblical, and similar names ending in a sibilant, especially if they are polysyllabic, do not take an added s in the possessive; among sources giving exceptions of this kind are The Times[9] and The Elements of Style, which make general stipulations, and Vanderbilt University,[10] which mentions only Moses and Jesus. As a particular case, Jesus' is very commonly written instead of Jesus's, even by people who would otherwise add 's in, for example, James's or Chris's; Jesus' is referred to as "an accepted liturgical archaism" in Hart's Rules.
Similar examples of notable names ending in an s that are often given a possessive apostrophe with no additional s include Dickens and Williams. There is often a policy of leaving off the additional s on any such name, but this can prove problematic when specific names are contradictory (for example, St James' Park in Newcastle [the football ground] and the area of St. James's Park in London). For more details on practice with geographic names, see the relevant section below.
Some people like to reflect standard spoken practice in cases like these with sake: for convenience' sake, for goodness' sake, for appearance' sake, for compromise' sake, for peace' sake, etc. This punctuation is preferred in major style guides. Others prefer to add 's: for convenience's sake.[11] Still others prefer to omit the apostrophe when there is an s sound before sake: for morality's sake, but for convenience sake.[12]
