How would you say "It takes one to know one" in Latin?

What is the most idiomatic way of saying “It takes one to know one” in Latin? Granted this probably isn’t a native expression in the language, but I’m sure it’s been rendered into Latin at one time or another.

My high school Latin is rusty, but maybe: Unus est postulo scio unus.

This is a tough one. This is about the best I can do.

Solus unus qui est potest unus scire. (Literally, “Only he who is one can know one.”)

Thanks for the replies so far.

Postulo and scio mean “I demand (require)” and “I know” respectively. You want the infinitive, scire for “to know” and the third person singular present active indicative for postulo would be postulat. I think you were going for * Unus est postulat unum scire* (“It requires one to know one”) but I’m still not sure that really works in Latin).

I have a small correction to make to my own sentence. My second unus should have been in the accusative case. All that means is that the s in the second unus should be changed to an um. My corrected sentence should read as follows.

Solus unus qui est potest unum scire.

I think it’s ok now.

How about:

tantum talis talem scire potest

(Lit. ‘only such a one can know such a one’).

How about facere est scire? Literally, to do is to know.

I must slightly amend my offering to

tantum talis talem cognoscere potest

which means the same thing literally, but in a ‘recognise/come to know’ sense of ‘know’, like the dif. between ‘je sais’ and ‘je connais’ in French.

On reflection, that’s not good Latin: we need gerunds: facendum sciendum est.

I don’t recall if esse has a gerund form, but if available, it might be more suitable: fuendum sciendum est.

I was thinking exactly the same thing about gerundives but couldn’t figure out what the gerundive would be for esse either. I tried essendum and futuendum but they didn’t look right.

Or how about something like “Necesse est sis talis ut cognoscas.”

Lit: It is necessary that you be such in order to know.

Sorry - forgot to add that I quite like Daphne’s. Cicero would be proud of the alliteration.

“Itway akestay oneway otay owknay oneway.”


There’s no gerund or gerundive for ‘esse’. To express necessity, ‘necesse est’ and variations (as in Helen’s example) is used.