[Note: This post was updated on May 15, 2026.]
Q: Which is correct: “I have no idea of the year, leave alone [let alone] the day”? I once came across an authoritative position on this, but I can’t remember the authority or, more importantly, what was authorized. I sure hope you can help.
A: The more common idiomatic usage in both the US and the UK is “let alone,” not “leave alone.” So the sentence would be more familiar to you if it read, “I have no idea of the year, let alone the day.”
However, both “let alone” and “leave alone” have been used in the sense of “not to mention” since the 19th century, according to citations in the Oxford English Dictionary. And “leave alone” is still sometimes used this way in British English. One is not more “correct” than the other, simply more common.
Interestingly, the phrases “let alone” and “leave alone” have also been used interchangeably over the centuries in two much older senses—one for going away from or abandoning someone, and the other for allowing a person or thing to remain undisturbed.
Here’s how the OED defines a sense of “leave alone” that dates from the early 14th century: “to leave (a person) alone: to go away from (a person) so that he or she is without company or support, to abandon or desert; to let alone.”
And here’s how the OED defines a sense that dates from the late 15th century: “to leave (a person or thing) alone: to stop or abstain from interfering with or paying attention to; to let alone.”
But getting back to the usage you’ve asked about, Merriam-Webster’s Dictionary of English Usage says that “leave alone” in the sense of “not to mention” is occasionally seen in British English. But even there it’s “a rather rare variant” of the more usual “let alone.”
(We briefly discussed “let alone” and similar constructions in a posting several years ago about the expression “not to mention.”)
Merriam-Webster’s says the phrase “let alone” is being used in this case “as a conjunction to introduce a contrasting example for purposes of emphasis.” Its meaning is close to “not to mention” or, in some negative contexts, “much less,” the usage guide adds.
In the OED’s view, “the imperative let alone” is “used here colloquially in the sense of ‘not to mention.’ ”
Oxford’s earliest citation is from an 1812 short story by the Anglo-Irish writer Maria Edgeworth: “I didn’t hide, nor wouldn’t from any man living, let alone any woman.” [The italics are the author’s.]
And this is the OED‘s earliest citation for “leave alone” used in the same sense: “There are not five, perhaps, who would have the grace to honour an angel, leave alone ten.” (From John Pring’s Kingdom Sermons, Second Series, 1838.)
Since we’re Jane Austen fans, we’ll end with an example from a letter she wrote to her sister, Cassandra, in 1816, apparently referring to two of their six brothers:
“He does not include a maid in the list to be accommodated, but if they bring one, as I suppose they will, we shall have no bed in the house even then for Charles himself—let alone Henry. But what can we do?”
With that, we’ll let it be.
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