I corrected someone using "navigatable" when they meant "navigable". They wanted to know why it is the latter. Does anyone know? Is there a reason?

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    The English language shuns reason every chance it gets... Dec 10, 2019 at 18:24
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    This seems to be common with adjectives derived from verbs ending in -ate. See: impregnable, abominable, irritable, innumerable.
    – 79037662
    Dec 10, 2019 at 18:27
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    @79037662 Rotable (not rotatable) conjugable (not conjugatable) demonstrable (not demonstratable)
    – Nigel J
    Dec 10, 2019 at 19:41
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    @NigelJ - Oh no!!! You mean there are exceptions to the rules of English???
    – Hot Licks
    Dec 10, 2019 at 19:58
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    @Hot Licks Britannia ruled the waves. Her ruler apparently wasn't that straight. Dec 10, 2019 at 20:04

2 Answers 2


I don't have an answer for why navigate yields navigable instead of navigatable; but in doing so, navigable is by no means a rule breaker among its closest peers. In fact, English has at least eight word pairs involving verbs with a -gate ending and adjectives with a -gable ending, as confirmed by The American Heritage Dictionary of the English Language, fifth edition (2010):

  • investigate --> investigable

  • irrigate --> irrigable

  • litigate --> litigable

  • mitigate --> mitigable

  • navigate --> navigable

  • obligate --> obligable

  • propagate --> propagable

  • segregate --> segregable

AHDEL doesn't list any similar -gable adjective form for a larger group of at least seventeen -gate verbs:

  • abrogate

  • aggregate

  • arrogate

  • castigate

  • conjugate

  • congregate

  • corrugate

  • delegate

  • derogate

  • elongate

  • fumigate

  • instigate

  • interrogate

  • relegate

  • subjugate

  • subrogate

  • supererogate

But on the other hand, it doesn't list any adjectives of the form -gatable. For these reasons, it seems fair to say that, within the subset of -able adjectives associated with verbs ending in -gate, navigable follows the standard pattern—the same one that the other seven -able adjectives associated with -gate verbs follow.

  • By the way, if I had to guess which of the seventeen uncommitted "-gate" verbs would be most likely to have an "-able" adjective of the form "-gatable" rather than "-gable," it would be elongate --> elongatable, simply because elongate is the only verb in the group in which the letter preceding "-gate" is a consonant rather than a vowel. There is something uniquely disturbing about the option elongable.
    – Sven Yargs
    Dec 11, 2019 at 9:44
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    I find castrable more disturbing. Dec 11, 2019 at 14:53

Wiktionary defines navigatable as a misspelling of navigable made from the verb “navigate” (possibly nonstandard):

  • 1992, Peter Sammartino and William Roberts, Sicily: An Informal History‎, page 45: Rivers were made navigatable, irrigation was improved, and the use of hydraulics was greatly increased.

  • 1998, Flexible Query Answering Systems‎3, page 83: The second is that it has potentials for information exploration, because the displayed network is navigatable.

Probably because of the common usage of the suffix -able often applied to verbs in English:

common termination and word-forming element of English adjectives (typically based on verbs) and generally adding a notion of "capable of; allowed; worthy of; requiring; to be ______ed,"


  • Thus hated, hateable. Debated, debatable. Rated, rateable or ratable. Navigated? Dec 10, 2019 at 20:02
  • @EdwinAshworth - it is a misusage, possibly non standard they say. Actually navigable entered the English language in mid-15C directly from French “navigable” (see link)
    – user 66974
    Dec 10, 2019 at 20:11
  • @user067531, why don't you incorporate that comment into the answer? It is much more directly responsive to the OP's wondering why navigable is the correct form than what is in the answer now.
    – jsw29
    Dec 10, 2019 at 22:54
  • I don't understand how a misspelling can be other than non-standard. Unless there's a broadened definition of misspelling: 'a spelling once considered incorrect, but now acceptable'. Which I'm not aware of. Mar 4, 2022 at 17:15
  • It entered from French, as mentioned. French etymology is off-topic, but French navigable comes from the French naviguer. Why there is a "t" in navigate is another question, but I'm inclined to blame Latin.
    – Stuart F
    Mar 4, 2022 at 17:22

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