Let alone

[MockneyReject]

I know it's function and when to use it. I can think of alternatives.
But AIBU to agree with DS(7), who says it doesn't make sense? That those two words together don't mean what they are used to mean? He just came across it in a book, and the more I look at it, the more 'wrong' it looks!
I can't come up with an actual definition that we're both happy with.
The best I can do is that it is correct, but that it doesn't actually make sense.

So, you can't explain it to your own satisfaction, let alone explain it to your son?

I think "let" in this sense is a synonym for "leave" (as in "don't disturb him, let him be"). So, "let alone" = "leave to one side".

My opening question above then paraphrases: "leave to one side for the moment the idea of explaining this to your son [the harder task]; you can't even explain it to your own satisfaction [the easier task]"

So, pattern is:

A is not possible / understandable / amusing / ... , let alone B.

B is something that would be considered even less possible / understandable / amusing / ... than A. "Forget about B, even A is not..."

Thank you DadDadDad.

I just couldn't see that, before.

Happy to help. I enjoyed puzzling out the logic. it is one of those constructions that I have to think about, like "not easily underestimated" - or is it "overestimated"?