There doesn't seem to be an English word describing the ability to tell truth from a lie. I've Googled, and posted on my FB account, but can't seem to find a word that precisely describes this ability.

  • Discernment. M-W defines this as "able to see and understand people things, or situations clearly and intelligently." Best so far, but a bit off the mark. It does not precisely identify the ability to perceive and separate truth from falsehoods.
  • The antonym of gullible
  • A discerning ear
  • (Slang) anti-bs meter; able to discern bullsh!t.

Others have suggested guarded, prudent, realistic, astute, and perceptive... but none of these precisely describe the quality that I've described.

The word should fit 'XXXXXXX' in the following:

John is so gullible; he'll believe anything. Not so Jane, she is XXXXXXX. She has quite the discerning ear; you'll never be able to deceive her with a lie.

Here are some possibles (consulted thesaurus.com; listed antonyms for gullible; definitions from Google.)

  • discerning. Having or showing good judgment. Discussed above; best so far, but a bit off the mark.
  • astute. Having or showing an ability to accurately assess situations or people and turn this to one's advantage. Rejected because does not account for lies.
  • knowledgeable. intelligent and well informed. Does not speak to distinguishing truth from lies.
  • perceptive. Having or showing sensitive insight. Does not speak to discernment of truth or lies.
  • suspicious. Having or showing a cautious distrust of someone or something.. Speaks more to distrust than separation of truth from lies.
  • unbelieving. Not believing someone or something. Does not speak to the ability to distinguish truth from lies.
  • 3
    From the title, I came here to post discernment. But you have already discounted it.
    – jejorda2
    Jul 14, 2017 at 20:55
  • This question is a single-word-request and as such needs to be edited to include a requisite contextual sentence to help us understand what the best word is to meet your needs. Since you have proposed a synonym/antonym, you should also show us that you have consulted a thesaurus and tell us why you have dismissed at least the very best examples as meeting your needs. The question may end up closed otherwise.
    – Tonepoet
    Jul 14, 2017 at 21:28
  • 1
    I hate this kind of question. I don't believe there exists some inherent trait or personality type that encompasses an ability to perceive that a lie is being told. That's a crock, as they say in my neighborhood. This is not an ability. One person could figure out if a particular person is lying in some instances, but not in others. Many factors come into play.
    – Lambie
    Jul 14, 2017 at 22:01
  • 1
    @Lambie, I see your point, but the fact remains that some people are much easier to fool than others. What is the adjective to describe one that is not-so-easy-to-fool?
    – kmiklas
    Jul 14, 2017 at 22:16
  • 2
    'Not so Jane, she's a veritable lie detector' is what I'd say, metaphorically comparing her to the machine.
    – Spagirl
    Jul 15, 2017 at 6:55

3 Answers 3


How about the word wisdom?

Def: The ability to discern what is true, right, etc. if you can discern truth then you automatically negate lies.

The use of the word discern in the definition also, in my opinion, doesn't pose a problem since it is defined as follows: if you discern something, you are aware of it and know it. ie the truth

Collins dictionary.

  • In my mind, wisdom has that King Solomon quality about it. I don't disagree that wisdom encompasses the ability to discern truth from lie, but wisdom embodies far more. I seek a term that more precisely describes the ability to discern truth from lie. Perhaps discern is the best that English has to offer.
    – kmiklas
    Jul 14, 2017 at 22:18
  • Thank you for your comment. Yes, perhaps wisdom is too general .
    – user242899
    Jul 14, 2017 at 23:32

I might suggest the word Sagacious

Sagacious combines some elements of "wise to the world" with the concept of a sharp and well considered use of intellect, as I understand the word

Sagacious at Dictionary.com adjective

1. having or showing acute mental discernment and keen practical sense; shrewd:

a sagacious lawyer.

  • 'Discerning' which is really your best choice, @kmiklas (because it connotes the ability to discern a truth from a lie) is also used to define 'sagacious' in this excellent answer and therefore 'sagacious' is another good option that fits your case. Jul 15, 2017 at 1:49

There doesn't seem to be an English word describing the ability to tell truth from a lie.

That is because English is an excellent language that realises that the ability to tell truth from a lie 100% of the time does not exist.

As a consequence, any antonym for gullible, which does not mean "always accepts a lie as the truth" is not going to encompass this idea of infallibility.

The nearest you will get is a reasonable approximation:


streetwise, adj.

Of a person: that has the skills and knowledge necessary for dealing with modern urban life; smart; tough. Of a thing: suitable for or reflective of modern urban life.

1949 P. W. Tappan Juvenile Delinquency xix. 538 She was streetwise enough not to get involved in the same area twice.


c. Cautious and careful in worldly or business matters; worldly-wise, shrewd.

1987 P. Wright & P. Greengrass Spycatcher vi. 73 In fact, the intelligence gathered was worthless. Khrushchev was far too canny a bird to discuss anything of value in a hotel room.

astute, adj.

Of keen penetration or discernment, esp. in regard to one's own interests; shrewd, subtle, sagacious; wily, cunning, crafty.

1878 R. B. Smith Carthage 331 He had, with the astute fickleness of a barbarian, come to a secret understanding with Scipio.

You will note that within the above definitions there are other close synonyms that you may find useful.

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