If you say somebody doesn’t let his left hand know what his right hand is doing, you’re saying that person is very sneaky and good at concealing his questionable deeds.
But that’s not the original meaning of the idiom. As far as I can tell, it first appeared in the New Testament (Matthew 6:3) and it was “when you give to the needy, do not let your left hand know what your right hand is doing, so that your giving may be in secret. Then your Father, who sees what is done in secret, will reward you.”
So the original meaning was about hiding good deeds. When did the meaning shift to mean hiding bad deeds?
I’ve never heard either of those. My understanding of the common usage is in reference to a large organization whose disparate elements are obliviously working in opposition to one another.
Both meaning are new ones to me. I’ve always seen it used in the context of poor communication within an organization or entity. Like the sales team pushing product A while the inventory team has a surplus of product B.
Okay, the idiom meaning concealing your bad deeds was the one I grew up on but I can’t find a cite for that usage with a quick search.
The meaning about concealing good deeds goes back to the New Testament and also appears in the Quran. It’s also one that produces dozens of cites if you try to look it up online because there are apparently a lot of bible study groups on the internet.
I found that there’s a usage that appears to have originated with Carl Jung, which means how the conscious mind might not be aware of what the unconscious mind is doing.
And there’s what appears to be the modern usage, which is how different parts of a group can be unware of what the other parts of the same group are doing.
I think that they are all connected - if your left hand doesn’t know the good deeds your right hand is doing, it’s also likely that your left hand doesn’t know the questionable deeds that your right hand is doing - which is really a special case of different parts ( the right and left hand) of an entity/group ( your body) don’t know what the other parts are doing.
I feel there are two different lines of meaning here. In one, there is a conscious concealment. A person who doesn’t let his left hand know what his right hand is doing is aware of what he’s doing; he’s just making sure nobody else knows, even people who are very close to him (as close as a metaphorical set of hands).
The second, more recent, meaning is about unconscious concealment. In this case either it’s a person who is unaware of what he’s doing unconsciously or an organization which has poor communications between its sections.
I’d bet the more common one morphed out of the bible verse cited. One is intentional & one is accidental but they are both about not everyone being clued in on a plan.
While Jesus’s use of it is about good deeds and therefore positive, I don’t see anything inherent in it that it is about good things. I suspect the same Aramaic idiom was used when concealing bad things, too.
And, well, bad deeds are the ones you are more likely to conceal than the good ones.
I’m sure this usage connoting knowledge of bad deeds being committed by or on behalf of someone while providing “plausible deniability” of such knowledge goes back way further than 1957.
This is my version, too. Though my version is probably a bit more expansive, as it also refers to duplicating work, rather than just working in opposition. Typically associated with a large organization and a lack of communication between different parts of it.
I’ve heard all three of the meanings; including the specific Biblical quote, but also both of the senses in the OP and also @Cervaise’s sense.
And I think, though am not certain, that all those meanings have been around all of my life. The biblical one, at least, has obviously been around a lot longer; maybe the others have too.
The whole idiom has always triggered my inner Sheldon Cooper. It doesn’t make. any sense. An individual’s hands can’t know things; they don’t have independent brains. And they certainly can’t keep secrets from one another.