I'm writing a lab for a simple diffraction experiment, and I am stuck on this grammatical point:

Is it more appropriate to say "Huygens' Principle" or "Huygens's Principle"*? A cursory glance at Google seems to indicate that the most common usage seems to be "Huygens' Principle"; but as the apostrophe is at the end of the word as in the plural possessive, my inner grammarian is screaming that it should be "Huygens's". Which is correct?

*I know it can also be rendered as the Huygens-Fresnel Principle, obviating the need for my query.

2 Answers 2


There is a degree of ambivalence between Huygens' and Huygens's. The Chicago Manual of Style says that either may be used, whereas Professor Strunk (The Elements of Style) insists it is Huygens's.

I personally prefer Huygens's, as it seems to more explicitly indicate the possessive. Your mileage may differ.

See Wikipedia on English possessive.

  • Huygens's Principle sounds fine to me, but some of my colleagues have declared it anathema. I think I will stick with Professor Strunk!
    – SteelAngel
    Jan 26, 2016 at 18:33

Depends on whom you ask!

Some grammarians say, "If the extra apostrophe s ('s) makes the word difficult to say, then drop it and stick with just an apostrophe (').

That makes sense to me, especially with words such as

  • Moses's roles as leader, prophet, lawgiver . . ..

  • Jesus's words of wisdom . . ..

  • These two leases's conditions state specifically that . . ..

Those italicized words would then become

  • Moses' roles as leader, prophet, lawgiver . . ..

  • Jesus' words of wisdom . . ..

  • These two leases' conditions state specifically that . . ..

Some grammarians say that "Rule are rules. Even if a word ends in s and the resulting apostrophe (which indicates the possessive) creates a tongue twister, you must still attach the apostrophe ('s)."

Still other grammarians say, "Who gives a crap? Do watcha gotta do. Just be consistent."

  • 1
    I like your answer! Jan 26, 2016 at 18:36
  • 1
    @Cyberherbalist. Thanks! I like yours's too! (Now wait a minute . . ..) Don Jan 26, 2016 at 18:38

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