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The Plural of Pendulum

If one consults a dictionary, one will find that the plural of pendulum is pendulums. The Oxford English Dictionary (2nd Ed) admits pendula as a rare and archaic plural. Most (if not all) other dictionaries do not even mention pendula as a possibility. It is unlisted.

On the other hand, a web search for "pendula" gives a huge number of hits (though not as many as for "pendulums"). In addition, the American Journal of Physics, The Physical Review, and many other physics journals have a significant number of (recent) articles which use "pendula" as the plural. In fact, quite a few authors use both plurals interchangeably. Sometimes one just sounds better than the other, perhaps. Though used less often, "pendula" hardly seems rare.

A review of several current introductory physics texts shows that just about as many use "pendula" as use "pendulums," and some use both. Though possibly not a true authority on the subject, it is also noted that the spell checkers on two popular office packages both allow pendula.

One argument is that pendulum was never a Latin word (though it is derived from a Latin word) and so to use the Latin plural is inappropriate. Using that same argument, one should disallow the "-ums" plural on words that are Latin—a practice which is not done consistently.

- BHS

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