If we use implausible as a stronger version of improbable, meaning "seemingly (but not absolutely) impossible", is there a word equivalently stronger than probable, e.g. "seemingly (but not absolutely) certain"?

A diagram of the level of certainty that I ascribe to various words:

impossible < implausible < improbable < possible < plausible < probable < ??? < certain

You can say almost certain, very likely, good bet, confident of, etc, but is there a single word?

Conclusion: thanks for all the suggestions. Yes, I do understand that possibility, probability, and plausibility have different connotations regarding belief, information, truth, etc. I stand by my assertion that they each can be roughly measured on a 0-1 scale, even if the qualities being quantified are not exactly the same.

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    presumable? – Peter Shor Mar 4 '15 at 22:16
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    Not sure if you'll get a single work, but how about highly plausible? – Minnow Mar 4 '15 at 22:18
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    Implausible tells you that something cannot happen. The opposite of this is that something can happen. In your diagram, you interpret the opposite as something that must happen, which is awkward. – Martin Krzywinski Mar 5 '15 at 0:43
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    You are on to a good comparison, but your probability/plausibility scales are not corresponding intuitively. – ScotM Mar 5 '15 at 0:56
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    "Implausible tells you that something cannot happen" totally incorrect. – Fattie Mar 5 '15 at 7:37

If we understand implausible to express "I cannot believe it", then it seems to me that its strong antonym should express "I cannot doubt it": so I propose indubitable.

A weaker contender might be unquestionable.

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    That's not what implausible means. – curiousdannii Mar 5 '15 at 12:12
  • @curiousdannii, they may not be the words your dictionary of preference uses to gloss the term, but I think they do a fair job of conveying the subtext of real-world usage of a term which Cambridge can gloss as difficult to believe and which typically expresses a subjective opinion. – Peter Taylor Mar 5 '15 at 13:30

The opposite of implausible is plausible.
The word that belongs on the right-most side of your plausibility scale is convincing.

I would tend to disagree about the relationship you have described between implausible/plausible and improbable/probable.

improbable: "It is unlikely."
probable: "It is likely."
implausible: "I cannot imagine that there could be a case in which this would be true."
plausible: "I can imagine that there could be a case in which this could be true."

(im)plausible is based upon belief and opinion, whereas (im)probable is based upon statistical fact. The level of plausibility is based strictly upon the depth of knowledge on the subject, gullibility, and/or faith of person providing the opinion. To someone, a thing could be implausible while still being certain in reality.

convincing: "I cannot imagine that there could be a case in which this would be false."

Convincing does not imply a certain outcome, but it does imply an individual's certainty by belief. Again, because you're trying to compare a subjective measure with a concrete measure, there will be oddities in definition. For example, a statistical probability that is certain is guaranteed to happen 100% of the time. Conversely, an individual can be certain about an outcome, yet still be proven incorrect.

An individual that is skeptical or closed-minded about a subject could have a plausibility scale measuring similar to this:


An individual that is gullible or imaginative about a subject could have a plausibility scale measuring similar to this:


A person's perception of a subject does not change the probability.

  • Using your formulation, I seek "I cannot imagine ... this would be false." – Foo Bar Mar 4 '15 at 22:48
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    You are seeking a word referring to a statement made with conviction. You should still be careful about creating the diagram as you have; (im)plausibility is not related to (im)probability and therefore cannot be charted in that way. – Ian MacDonald Mar 4 '15 at 22:54
  • Ian, this is a valid complaint about the formulation of the question, but does not include any attempt at an answer. If you propose to define implausible more concretely as "I cannot imagine that there could be a case in which this would be true," then the original question, which asks for a word at the other end of the spectrum, can be interpreted as looking for a single word that means, "I cannot imagine that there could be a case in which this would be false." Any ideas? – Josh Mar 5 '15 at 3:23
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    I gave it some more thought and I came to the conclusion that convincing is the answer. – Ian MacDonald Mar 5 '15 at 3:54
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    I believe you have failed to read the answer to the end. Not only does it answer the question posed in the title of this page (as plausible), but it offers an answer to the question posted in the body of the page (as convincing). – Ian MacDonald Mar 5 '15 at 4:40

Conclusive is at the most convincing end of the argument scale:


(Of evidence or argument) serving to prove a case; decisive or convincing:

Plausible is less convincing:


1 (Of an argument or statement) seeming reasonable or probable:

Implausible is still less convincing:


(Of an argument or statement) not seeming reasonable or probable; failing to convince:

Inconceivable is still less convincing:


Not capable of being imagined or grasped mentally; unbelievable:

The corresponding possibility scale would be certain, probable, improbable, impossible.


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    Scott introduces the overwhelming point here. "plausible" (and implausible) refers only to a statement or argument, NOT to a happening, concept or event. – Fattie Mar 5 '15 at 7:41
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    Kudos for being the first to focus this question toward an intelligent answer! – Good A.M. Mar 5 '15 at 23:15


the opposite of implausible is plausible.

Note that your diagram is totally wrong. plausible and implausible are equally far from the center.

(If you feel they are not, you're just not familiar with the words.)

Note that the words certain, probability etc, on the diagram, have no connection to anything at all. "plausible" (and implausible) refers only to a statement or argument, NOT to a happening, concept or event.


You could go with the Mythbusters spectrum:

  • Busted (= Implausible)
  • Plausible
  • Confirmed.

I can't think of a broad, general purpose word that suggests very strong likelihood. Depending on the context I might consider words like: undeniable, irrefutable, compelling, expected, probable, or simply likely. (Yes, these latter two can just mean "more likely than not," but can have a stronger connotation depending on the context.)

Keep in mind, though, that "implausible" when used precisely has a meaning more like unbelievable than improbable - specifically, "Not having the appearance of truth (an implausable alibi)". That is, if you tell me something I don't believe and I say it's improbable I'm probably questioning your factual knowledge, but if I say it's implausible I might be questioning your honesty.



What was once merely plausible, is now accepted as the truth.


I would go with certain or confirmed, depending on circumstances. Something which is implausible is not believable. That which is plausible is believable but not necessarily true.

If someone has provided an explanation or alibi, and it is proven to be true, you would say that the alibi has been confirmed.

"His alibi is wildly implausible."

"His alibi is plausible, but we need to investigate it further."

"His alibi has been confirmed."

If you are making a prediction, you could say

"War with Japan is most implausible." (Although unlikely would probably be used here.)

"War with Japan is a plausible consequence of this policy, but is deemed unlikely."

"As a result of the attack on Pearl Harbor, war with Japan is certain."

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