Hi,
We all know that there is a verb for telling a lie. But what is the verb for telling the truth? If there is none then why there is none?
My mother language is Spanish. In Spanish there is also a verb for telling a lie (“mentir”) but there is no verb for telling the truth.
Thank you!
Interesting question. We have to attest and to aver, but these both mean “to allege as fact”.
We do have the adverb “truthfully”. Compare:
"I paid already," he lied. Explicitly untrue.
"I paid already," he said. Could be true or untrue.
I paid already," he said truthfully. Explicitly true.
I suppose “to verify” might do it?
There appears to be a verb to truth 
.
Merriam-Webster offers only the following as “near antonyms” for the verb “lie”:
assert, swear, testify; authenticate, confirm, substantiate, validate, verify
There are no direct opposites, apparently. Clearly, the Straight Dope needs to generate such a verb. I propose “to washington” in honor of our cherry-tree-chopping president. Any others?
It requires a verb phrase, which isn’t at all unusual in English. The opposite of “he lied about it” is “he told the truth about it”.
See Dictionary.Com for tell the truth
He lied. He _____________?
Thruthinessized.
coultered?
Oh, sorry. You want an antonym.
He told the truth. As Liberal said, you need a verb phrase because there is no single verb.
I will follow Stephen Colbert’s lead, and suggest truthicate.
The opposite of prevaricate would be postvaricate. No?
He didn’t lie, he obfuscated.
He Lied. He !lied.
Is there a single word for telling the truth in any language? I’d wouldn’t be surprised if there wasn’t. Isn’t the default state “truth” and we only need a special verb to indicate a deviation?
“Truthin’” *
As Nancy Sinatra sang it "You’ve been lyin’ when you outta been truthin’*"
From These Boots Were Made For Walkin’
I can’t think of any in spanish, right now. There are translations to all the words mentioned so far, but none of the is really “truthicate”.
“aseverar” means “to state as truth”. That makes it closer to assert than anything else, I guess.
Candidly, forthrightly, honestly, etc., could be used to modify/clarify a verb of your choice.
i.e: " He candidly stated …
Interesting. There seem to be no good opposites for “cheat” either.
I think you are on to something; what is the opposite of “steal”?
When you think about it, there’s no concept that is the opposite of “steal”. However, “purchase”, “return”, and “accept” can all be antonyms in certain circumstances.
He stole the book.
He purchased the book.
He stole the lawnmower.
He returned the lawnmower.
He stole the present from his great aunt Ruth.
He accepted the present from his great aunt Ruth.