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What’s the rule to decide whether you add -er or whether you add -or when creating a noun from a verb?

Sometimes it’s -er:

  • read > reader
  • hate > hater
  • hit > hitter

But other times it’s -or:

  • meditate > meditator
  • collect > collector
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up vote 39 down vote accepted

This has been previously touched on here: “Commentor” vs “Commentator”. I'll try to expand on that.

Both -er and -or are so-called "agent noun suffixes", and Wiktionary has entries for both:

Generally speaking, -er is much more common in English (which should come as no surprise since it has deep Germanic roots, see the link) and can be easily attached to any English verb to form the corresponding noun (drivedriver, runrunner, drinkdrinker, etc.).

The suffix -or, on the other hand, comes from Latin, and is used much more seldom, basically where Latin would do it. Just try building the words drivor, runnor or drinkor, and see for yourself. In fact, Wiktionary lists only a handful of terms that were derived using this suffix, such as actor, author and sculptor, and goes on to provide the following usage notes:

English generally appends this suffix where Latin would do it—to the root of a Latin-type perfect passive participle. For other words, English tends to use the suffix -er. Occasionally both are used (computer vs. computor).

Etymonline has additional info on the origin and usage of -er and -or.

Edit: courtesy of Martha, here's a link to a post on the "Separated by a common language" blog that provides further details and addresses the differences between US and UK English:

The -or suffix is primarily found in words derived from Latin, whereas -er can be put on the end of just about any verb that involves an agent (a 'doer' of the 'action'). But Latin-derived words differ in how strongly they are associated with the -or suffix. Latin-derived verbs that end in -ate, for example, almost always take the -or suffix. So we have dictator, but not a variant *dictater, alternator but not *alternater.

Things are less clear-cut with other Latin-derived verbs. For example, in my job, I advise students and convene courses, and when I spell out those roles, I'm an advisor and a convenor, but when my UK university spells them, I'm often an adviser (which just looks wrong to me) and a convener. [...] The -or form is stronger in the US than the UK, though there's considerable variation within each country.

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They both come from a PIE agentive suffix with two variants (ablaut grades): *-ter, the E-grade, meant a person who had performed some action, while *-tor, the O-grade, meant a person who generically performs some action (i.e, a professional). It's the difference between simple description (the murderer) and occupational generic (the pitcher for this game). Of course, that was in PIE. In English it's a tossup which spelling it has, but they're all pronounced the same, so the spelling is irrelevant. – John Lawler Mar 20 '15 at 18:48

The best rule I've found?

If you can change the word to have "ion" at the end, it is OR. If you can't, it's ER.

TeachER (can not be teachion) ConductOR (conduction) ProfessOR (profession)

I can't really think of any ER's sorry!

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It's far from a perfect rule, however; consider investor, proprietor, creditor / debtor, ambassador, victor, conspirator, juror, and vendor among others. – choster Nov 13 '13 at 18:35
I agree with choster except for conspirator which can be changed into conspiration – user61249 Jan 3 '14 at 19:32
I actually think this is a good rule of thumb. These words also tend to allow -ive suffixes. It is by no means perfect and there are many exceptions but for common words it works fairly well. act-action-active-actor, emote-(e)motion-(e)motive-motor, instruct-instruction-instructive-instructor. Note "propriet(e)", "ambassad(e)", "vict(e)" and "jur(e)" are not words, let alone verbs although we do have evict-eviction-evictor. – CJ Dennis Dec 9 '14 at 1:06
About 40 years ago I read that for neologisms "er" should be use used for human agency and "or" for mechanisms. This rule seems to fit much of the computer terminology that has been created since then. – Hot Licks Mar 20 '15 at 17:51

There are no 'rules' — that alone enhances the richness of this language.

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No reason to muss up singular and plural. – ceving Jul 13 '12 at 16:22
RedDwighT's explanation sounds complete and perfect. In addition, he himself added, "there are no 'rules'." Try to copy the word (er or or) of the others, instead of say or write in the way of yourself, that is what I can say and will do. – Jiancheng Zou Mar 13 '13 at 12:31

protected by tchrist Jul 1 '14 at 0:55

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