I find the distinction that MacMillan makes between not to mention and the supposedly synonymous let alone and still/much/even less useful: The phrases let alone and still/much/even less reinforce a negative or unlikely statement that precedes them. The still/much/even less constructs reinforce the negativity of the preceding phrase by subtraction -- Negative statement, still/much/even less ...
In "Let's get started", the starting point is in view and "Let's get going", you are on the starting point already. Moreover, there is a sense of extra involvement abundantly made clear by the sentence, " Let's start going".
The let alone construction has been analyzed in great and precise detail in a famous paper by Fillmore, Kay, and O'Connor: " Regularity and Idiomaticity in Grammatical Constructions: The Case of Let Alone ", Language, Vol. 64, No. 3 (1988:501-38). EDIT: By request. The two clauses have to be on a certain scale of meaning; one of the clauses must describe a situation that is less on that scale ...
As a rule, we don't use the passive voice with "let". "Allow" or "permit" is normally used instead: We were allowed to do whatever we wanted. We were permitted to drive the vehicle. Accordi...
Let go or be dragged. This is a saying often associated with Zen Buddhism (occasionally Stoicism). As far as I can tell, there's no historical connection, and it might well be originally English. ...
quotes - Origin of the saying "let go or be dragged" - English Language ...
Many people use "let, let's and lets" in conversation What's the difference between them?
meaning - Difference between Let, Let's and Lets? - English Language ...