Recently, a colleague became flustered when she used orientate instead of orient. She says she frequently makes this sort of "back formation error" because of the nominal form, which is orientation. This has gotten me thinking about how nominal forms are created.

Certainly, it is unambiguous for words that end in -ate or -ite (I think):

hibernate becomes hibernation
ignite becomes ignition

And some words, you need the "a" to pronounce the word easily:

cancel becomes cancellation
affirm becomes affirmation

But what about other words? Is there a difference in meaning between the suffixes -ation and -tion? Is there a rule about when to insert an a, and when to leave it out?

prevent becomes prevention
inspect becomes inspection
prohibit becomes prohibition
indent becomes indentation (not *indention)
cohabit becomes cohabitation (not *cohabition)
orient becomes orientation (not *oriention)

Do words that have the -ation suffix have an archaic -ate form? Are they related somehow?

NB: I know that orientate is considered a "real" word, but its use is considered uneducated by the hoity-toity academics with whom I work.


2 Answers 2


The Latin suffix -io, stem -ion-, is usually added to the supine stem ( ~= past participle stem) of a Latin verb, in order to form a noun of action (meaning "x-ing"). It is sometimes also added to other stems, but usually not. The verb vocare ("to call"), present stem voca-, supine stem voca-t-, gets vocatio ("calling"); the stem of that noun is vocation-, which is what our suffix was based on.

Because the regular suffix for the supine stem / past participle is -t- in Latin, we often see -tion; but compare also miss-ion, fus-ion, cohes-ion, inflex-ion, etc.. The same suffix can also be found with non-supine stems, though less frequently so, like rebellion, legion, etc.

Now how can we predict what comes before -ion in English? I don't have a neat system based on tight rules, but perhaps I can give a few general directions.

What we could do is try and think of a cognate verb, as you have been rightly doing. Does this verb end in vowel + t or vowel + te? If yes, it is probably based on a (real or reconstructed) Latin supine stem; then -ion can come right after the t, as in inhibit, complete, migrate.

And what if the verb does not end in vowel + t(e)? Then you need to know whether or not its stem is a supine stem in Latin. There is no way to know this except by consulting a Latin dictionary. But there are some unreliable rules.

Irregular supine stems most often end on s or x, so verbs like flex (from verbal stem flect-, "to bend") and fuse (from verbal stem fund-, "to pour") contain the supine stems flex- and fus-, leading to inflexion and fusion. But vex- and pos- are not supine stems, so vexation and position, from supine stems vexa-t- and pos-i-t- (the i is probably a fused theme vowel).

There are many supine stems that end on -pt- or -ct-, like act- and rupt-, leading to action and eruption.

Verbs ending on -nt are nearly always based on the present-participle stem -nt-, and so cannot get -ion right after nt; but there are a few supine stems on -nt- as well, mainly vent- and tent-, leading to -vention and -tention.

But there are also some nominal ("noun") stems that can get -ion, as mentioned before, like mens, "mind", stem ment-, leading to mention; and dens "tooth", stem dent-.

Cohabitation is an apparent exception. But both habē-re ("to have") and habita-re ("to inhabit") exist as verbs. Habitare was actually formed based on the supine stem habit- from habēre; then a new supine stem was formed based on this new verb, habitat-. And so we have pro-hibi-t-ion and co-habi-t-at-ion.

Normally it isn't very functional in Latin to make a new verb based on the supine stem of another, since you already have the original verb; but it is sometimes done, often to add a sense of frequency or intensity, and so two supine forms may come to exist. Usually a is then added after the supine stem to turn it into a new verbal stem, because a indicates a causative verb, i.e. a verb that means not "to do x" but "to cause someone to do x" (with nominal stems, "to turn into x, to affect with x", or simply to turn any nominal stem into a verb). So fugere = "to flee"; fugare = "to make flee, to drive away"; donum = "gift", donare = "to present as a gift" (or simply "to give").

Cf. haerē-re ("to stick") => hae-s-us (past participle, "stuck") => hae-s-ere => hae-s-it-us => hae-s-it-are => hae-s-it-at-us => hae-s-it-at-io =>> hesitation. Notice that the same supine suffix has been added thrice: s, it, at (the t was turned into an s after certain verbal stems; the i and the a are theme vowel and causative vowel, respectively). And so we have co-he-s-ion and he-s-it-at-ion, both from the same verbal stem haer(e)-.

So it is theoretically possible to add -ation after any supine stem; but that is usually not done, because just -ion is shorter. After any stem that isn't a supine stem, just adding -ion is unusual, so we will usually have to turn it into a (real or hypothetical) verb first with -a-, then add the -t-, then -ion — i.e. we have to add -ation. But, as mentioned above, there are many exceptions, where -ion can be added directly to non-supine stems; however, this is a fixed set of words that mostly already existed in that approximate form in Latin.

  • Excellent. You have covered the gamut, but you had me at supine stem. And I wish I could give you +5 for the hesitation example. Brilliant. Thank you!
    – Kit Z. Fox
    Sep 2, 2011 at 11:39
  • So basically, what you say is: This construction comes from supine verbs in Latin, but when it comes to non-supine verbs, you haven't the foggiest why people sometimes add -a, and at other times just -tion. Doesn't seem like it much answers the OP's question, to me. Sep 3, 2011 at 14:11
  • @KylePearson: Uh, no. The English suffix -ion can only be added to supine stems; whenever we have a word on -ion in which the suffix comes immediately after a non-supine stem, this suffix was added in Latin, not in English. The suffix is not productive in English in such cases; we have no choice but to add -ation to those stems. If the word was formed in Latin, both formations were possible, though you will usually see -ion with supine stems and -ation/-ition with non-supine stems, the many exceptions notwithstanding. Sep 4, 2011 at 0:11
  • @KylePearson: But I agree that this leaves open the causes of the many exceptions. As to the addition of -ion to non-supine stems, this is a question about Latin, not English, since I believe it nearly always happened in Latin. As to -ation after supine stems, some of those instances were also formed in Latin; others were perhaps formed in English—and I have not explained their origin, as you say. But how many of those are there anyway? It would be interesting if you could come up with a few (I expect there to be few). I didn't quite understand your hypothesis, but it could be worth while. Sep 4, 2011 at 0:19
  • From a phonological standpoint, the "exceptions" aren't exceptions at all; they clearly adhere to basic rules about emphasis and cadence, and these rules are usually quite easily intuited, if not explained. Sep 4, 2011 at 3:09

While "orientate" may be a back formation, it has been considered a legitimate word since the 1820's; it is often used in orienteering and surveys, and is a perfectly acceptable alternative to the verb, "orient".

The insertion of an "-a" or "-i" suffix between "-tion" and the preceding syllable is a consequence of two things:

  • The relative emphasis of the preceding syllable (is it lightly emphasized, strongly emphasized, or de-emphasized?)
  • and the final consonant/vowel array.

If the final syllable is anything but the most strongly emphasized syllable in the word, then generally "-a" or "-i" will be added to provide a strong vowel sound just before the "-tion" suffix. This is necessary because most standard nouns in English carry a light emphasis on the next-to-last syllable.

If the final syllable is strong, or if the next-to-last syllable is strong -- as in "prevent", or "indent" (i.e. -- is a two-syllable verb form) or "prohibit" or "inhibit" (i.e. -- a three-syllable verb form) -- then an "-a" is not needed ("indention" and "indentation" were established as words right about the same time, although "indention" did come a little after "indentation"; both are listed as legitimate words in dictionaries, and neither is considered a back-formation of the other by the online etymological dictionary).

"Cohabit" is a ringer because "habitate" is the original root, from "habitare" in Latin, so "cohabit" is the actual back formation, while "cohabitate" and "cohabitation" are the original forms.

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