I'm having a hard time understanding the idiom 'to say nothing of'

Question

One idiom that's been confusing me for some days is 'to say nothing of'. The Free Dictionary gives entries such as 'not to mention someone or something' and 'not even considering or mentioning the full significance of something or someone'. I'm not sure what the general meaning of the idiom is. Does it mean 'in addition to the subject being mentioned' or does it mean 'this subject fails to provide sufficient context to make the overall meaning clear'?

Here's another definition and example sentence I've looked up on Wiktionary.org:

"to say nothing of

Definition: (idiomatic) An apophasis used to mention another important, usually related, point: not taking into account, not to mention, without considering.

Example: She had already eaten a large lunch, to say nothing of a full cooked breakfast that morning"

I'm still confused about this idiom's meaning.

Answer 1

Apophasis?  I'm not going to talk about that. 

Of course, having said that, I've implied that there is something to be said.  You might find yourself imagining what I could have said -- not to mention that whatever I could have said must be something that supports my point very well, perhaps even more eloquently than anything I did put directly into words. 

Was she full?  She had already eaten a large lunch.  That's enough support for the idea right there.  Anything more would be beating a dead horse that had already crossed the finish line before it fell.  The further support of an extensive breakfast isn't even needed, is it? 

Then again, maybe the large lunch isn't enough support for you.  That phrase "not to mention" suggests that the lunch should have been enough, but, even if it isn't, there's more.  Breakfast happened, too. 

I lied.  I did talk about apophasis.  Paradoxically, I have to mention "her breakfast" in order to say "I won't bother to mention her breakfast."  That's defining apophasis through example.  Before that, I defined it through description.  Before that, I defined it through its likely effect. 

Apophasis.  Did I even need to talk about it? 

Answer 2

It's a pretty silly idiom, come to think of it. The way it works is thus:

Someone has a point. To support the point, the person says something in the form: "X, to say nothing of Y." (An alternative and equivalent phrasing is: "X, not to mention Y.") X is their main argument. Y is another argument that they could add to further support the point, but they're purporting to say nothing of, i.e. not mention, Y, which is of course absurd, because in the course of stating Y out loud, they're mentioning it. In any case, the idiom is such an ingrained part of the language that I dare say most people don't notice the self-contradictory passive-aggressiveness, rather treating the expression as pretty neutrally indicating: the main support for a point is X, and Y is extra support.

Example:

I was broke. I had a negative balance in my bank account, to say nothing of the money I owed to friends and family.

X is the negative bank balance, Y is the debt to friends and family. The point is, I'm broke.

Answer 3

The expression "to say nothing of" is best understood in terms of its function rather than their meaning, that's to say, when we use it and why, so I'm not going to try to and define it, but I will give examples -- and better ones than the sources quoted in the OP.

It's used when giving an example of something, or evidence of something, and saying that there are other possibly better examples that for some reason weren't used. Often the reason is that it's inappropriate to mention the other thing, or it's based on less reliable evidence, or even that you forgot about it until just now.

Consider a situation where someone gets an undeserved promotion at work. Someone who is surprised by it might say:

I can't believe Shelly got promoted from school receptionist to director! She doesn't have any experience in education or management at all, to say nothing of her terrible attitude.

In this example, it's normal to bring up someone's lack of relevant experience, but it's a bit inappropriate to attack someone's personality.

Or consider a different reaction to the same situation:

Shelly's the new director? She has no education, to say nothing of how she buys herself lunch from petty cash.

In this second example, it's true that she has no education, but we don't know for sure that she steals money from petty cash, so this information is less reliable.

I've never heard the word "apophasis" before now, so I can't say if it's a proper usage, but I'm guessing it's mentioned here because we use this expression to say things without fully committing to them, or at least acknowledging that they're not the best things to say.