In software development we use the word Assert frequently. While working I had to describe some of the code I was working on. I was going to write that...

This function makes the assertion that x is expected to be y.

While writing the sentence, which I actually have not yet finished, I had the realization that I could also write...

This function makes the assertation that x is expected to be y.

I got stuck trying to figure out if there was a difference between the two words:

  1. Assertion
  2. Assertation

I noticed quickly that assertation is red-lighted by my spell-checker, however, I was positive that assertation is a word. I did the obvious thing to do for any similar situation, and referred to a dictionary (I like Webster, so that's what I used).

Here is what the Webster American English Dictionary had to say:

Definition of Assertion

: the act of asserting or something that is asserted: such as

  • a : insistent and positive affirming, maintaining, or defending (as of a right or attribute) an assertion of ownership/innocence
  • b : a declaration that something is the case He presented no evidence to support his assertions.

  — Webster Dictionary

Definition of Assertation

  • : the act of asserting or something that is asserted : assertion

  — Webster Dictionary

At this point I still can't find a difference, or at least I don't see one. I also don't understand why assertation is being flagged by my spell checker, because the Webster online dictionary shows assertation being used in all sorts of published articles & documents.

Does anyone know if there is a reason I shouldn't use assertation, or if there is a difference between the two words? The only thing I can think of is that either: The difference is contingent on context, one is preferred by British English speakers, or that there is no difference.

If there is no difference, any notes on why there are two versions would be helpful.

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    I'd go with the shorter of most choices, but Americans often swing that way. Also, since I hear conversate (from conversation), I'd be scared of assertate coming back at me. Mar 25, 2022 at 15:46
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    It's not uncommon for use of a normal term in a novel environment to reset the morphology, like Toronto Maple Leafs instead of Leaves. This may be done on purpose, the way Grice coined the term implicature (instead of implication, which already had a formal meaning) for propositions derived from the conversational context instead of the meaning. Mar 25, 2022 at 15:55
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    As for why "assertation" is flagged: although it got a dictionary entry, it's orders of magnitude less common Mar 25, 2022 at 16:02
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    I have never seen assertation in my entire life and frankly, I could care less if it is in the dictionary. Lots of things are in dictionaries. That doesn't mean we use them...
    – Lambie
    Mar 25, 2022 at 16:24
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    @YosefBaskin Thats actually a really clever point.
    – JΛYDΞV
    Mar 25, 2022 at 16:34

4 Answers 4


From Robert Hartwell Fiske's Dictionary of Unendurable English:

assertation Misused for assertion.

  • I would dispute your assertation. USE assertion.
  • I can't say enough that this assertation is categorically, absolutely, and unconditionally wrong. USE assertion.
  • Given Miller's assertation that he knew of "at least three" teams willing to pay Boozer's $10.97 million salary, it appears that other teams have called to inquire about the forward. USE assertion.

Assertation, a thoroughly obsolete word used by fearfully modern people, is incorrect for assertion. Assertation—like the equally preposterous documentate (instead of document) and opinionation (instead of opinion)—is spoken or written by people who do not well know the words they use, by people who do not often read, by people who do not cavil over adding a syllable or two to a word: humanity lies elsewhere.

There's no difference between the two words, but I would use the more common1 2, rather, correct term, i.e., assertion.

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    Wow, this answer offers far more than I ever expected from an answer. My understanding, from reading the answer above, is that assertion is constructed from contemporary syllables, where assertate is an older implementation of the same same word. A modern English speaker, especially those who study English, should not use older implementations of words, because it doesn't help to progress society, or the English language. In fact, the use of such words, can hinder progressiveness, consequently; the use of assertate is actually frowned upon by some.
    – JΛYDΞV
    Mar 25, 2022 at 17:54
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    This is a fabulous answer! I really appreciate you taking the time to answer my question.
    – JΛYDΞV
    Mar 25, 2022 at 17:55


† assertation, n. Obsolete. rare. Affirmation, assertion.

a1535 T. More Wks. (R.) 141 (R.) Bothe ye confuting of theirs, and..the assertacion of our owne.

And Google Ngrams: assertion,assertation

  • Obsolete and rare? Mar 25, 2022 at 16:55
  • You tell me.... The Ngram is there...
    – Greybeard
    Mar 25, 2022 at 17:09
  • As obsolete as hens' teeth. Mar 25, 2022 at 19:08
  • But may still be used in historical novels, etc. i.e. rarely
    – Greybeard
    Mar 26, 2022 at 10:50
  • 'This function makes the assertation that x is expected to be y' famously appearing in Emma? Mar 26, 2022 at 17:44

A review of Google Books results for "assertation" shows a niche use: many of the results are from 1970s-1980s works in psychology about "assertation training." This seems to amount to a usage similar to "assertiveness," and indeed "assertiveness training" is found with a similar spike in the same time period.

If the question is "then why choose 'assertation training'" over "assertiveness training": I can't find enough material to verify, but I might speculate that such authors felt that "assertiveness" could be perceived as a character trait, but "assertation" as an activity or skill (and wanted to avoid "assertion" because they were differentiating between "an assertion," an individual expression, and "assertation," presumably a pattern of behavior).


Simply, British English... Assertion is the belief a stament is true, whereas, Attestation is the fact of a true statement.

Assertion, noun. A statement that you strongly believe is true.

Attestation, noun. A formal statement that you make and officially say is true.

I hope this clears it up.

  • 1
    Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.
    – Community Bot
    May 3, 2023 at 1:48
  • Hello, Dee Tee. The question doesn't mention 'attestation'. May 3, 2023 at 11:34

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