For brevity, I symbolise synonymity with .  So  X ≈ Y  means  X and Y are synonyms.

From http://www.thefreedictionary.com/let+alone: let alone ≈ not to mention

From Merriam Webster: let alone ≈ much less ≈ still less.

Are these all synonyms? What are the similarities and differences between each?

  • 1
    I've been speaking this language for 60 years, and never thought much about these four phrases as being synonyms. Very nice question! Commented Aug 28, 2013 at 17:21
  • 1
    @Cyberherbalist maybe because they are not really synonyms, there are subtle differences.
    – terdon
    Commented Aug 28, 2013 at 17:51
  • 1
    Oh, sure, @terdon, there is no such thing as true synonyms, IMHO, or at least there are very few. There are shades of meaning everywhere you look. Commented Aug 28, 2013 at 21:38
  • 3
    There is also "≈ never mind".
    – Pacerier
    Commented Mar 3, 2016 at 17:41

4 Answers 4


MacMillan and I agree in disagreeing that not to mention and let alone are synonymous:

not to mention: used for adding a comment that emphasizes the main idea of what you have already said: The weather here is gorgeous, not to mention the wonderful food.

let alone: used for saying that something is even less likely to happen than another unlikely thing: I hardly have time to think these days, let alone relax.

still/much/even less: used after a negative statement in order to emphasize that it applies even more to what you say next: I am no one's spokesman, much less his.

You could make the case that let alone and much less are synonymous, since you could substitute one for the other:

I am no one's spokesman, let alone his.

I hardly have time to think these days, much less relax.

However, substituting not to mention and let alone for each other would result in sentences that sound contradictory:

The weather here is gorgeous, let alone the wonderful food.

I hardly have time to think these days, not to mention relax.

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 a similar manner, let alone reinforces the unlikeliness of the preceding phrase with an even more unlikely scenario -- I couldn't get a date with a reanimated corpse, let alone the prom queen.

Some grammarians insist that not to mention and let alone are synonymous; while you can find some cases where substituting one for the other might make sense, I generally find their meaning and usage distinct from each other.

  • 5
    "Not to mention" is one of the more interesting contradictions, because it is always followed by the thing not to be mentioned.
    – ZZMike
    Commented Aug 29, 2013 at 4:36
  • I expounded further on still/much/even less, but remain unconvinced that they are synonymous with not to mention.
    – Gnawme
    Commented Aug 29, 2013 at 17:47
  • @Gnawme, "The weather here is gorgeous, let alone the wonderful food."? Is that even grammatical; it sounds odd.
    – Pacerier
    Commented Mar 3, 2016 at 17:43
  • I think your problem arises not from your adequate analysis of variations in meaning between the phrases, but from your lack of consideration for what it means to be a "synonym". To be a synonym does not mean that two words or phrases will always have the same meaning or usage in every possible context, nor that every nuance of connotation will be identical. In fact, it is very rare to find two words that are exactly the same nuance of meaning for every usage (those differences in connotation are often why we maintain so many synonymous words in the first place).
    – Daniel
    Commented Mar 22, 2018 at 3:16
  • Instead, an examination of a list of synonyms for pretty much any word (or phrase) will yield a spectrum of meanings, where some words are indeed very close in meaning for most contexts, and where others are only somewhat similar in meaning for very narrow contexts. If you think of any two words as having a range of usages, definitions, and connotations that can represented by a circle, to be a synonym only indicates there is some overlap somewhere between the two circles, as one would represent in a Venn diagram. By such a standard, "not to mention" and "let alone" are definitely synonymous.
    – Daniel
    Commented Mar 22, 2018 at 3:21

There is a fallacy at the heart of this question.

Let's say word W has two meanings W1 and W2.
The meanings may be completely different, slightly different, or merely different nuances.
The point is that W1 and W2 are different meanings and may be used in different contexts.

Word W also has three synonyms (S1, S2, S3) listed in various dictionaries, thesauri, etc..

As it happens:

  • S1 is a synonym for meaning W1 of word W
  • S2 & S3 are synonyms for meaning W2 of word W.

Therefore, although

  • S1, S2, & S3 are all synonyms for word W

it does not follow that

  • S2 & S3 are synonyms for S1

because they relate to different meanings of the original word.

Hence just because:

  • not to mention and let alone are synonyms; and
  • much less & still less are synonyms of let alone

it does not follow that

  • much less & still less are synonyms of not to mention.

[I am specifically not commenting on whether or not the cited words are synonyms - and they could be. I'm merely explaining that, on the basis on the facts given in the question, it does not necessarily follow that they are all synonyms of one another.]

  • I have not voted, but I think it's unwise to talk about lexical meanings as if they were countable, let alone easily distinguished. Any logical trail that starts with such a supposition winds up as breadcrumbs in the anthill. Though I have to agree that it's an interesting exercise to look up one expression in one side of a bilingual dictionary and then track down each of the phrases given back in the other side. Then when you track all of these down (they don't usually expand the way you might expect) again on the other side, they often coalesce into just a couple. Commented Aug 28, 2013 at 21:48
  • @JohnLawler I was treating them as 'countable' (if I understand you usage correctly) ONLY for the purposes of explaining my point. I agree that, of course, it is not that simplictic. But it struck me that the whole basis for the question assuming that all 4 are synonymous (see last 2 lines) was false.
    – TrevorD
    Commented Aug 28, 2013 at 23:11
  • I address this in more detail above, but you are on the right track here for finding the fallacy of assumption in the original question. Furthermore, there is the implied fallacy that synonymity implies nearly exact meaning and connotation for all usage cases. This is not the case. Synonyms only need be near or similar in meaning, not wholly equal.
    – Daniel
    Commented Mar 22, 2018 at 3:24

I would like to point out that these are not really synonyms but represent a decreasing scale of likelihood or relevance:

I could not afford a bicycle, let alone a motorbike, much less a car and still less a limousine.

To me, not to mention is not in the same group, it is used slightly differently as explained in @Gnawme's answer. For example,

The food was excellent, not to mention the wine!

  • So where does "never mind" fall in?
    – Pacerier
    Commented Mar 3, 2016 at 17:45
  • @Pacerier it doesn't, really. Never mind is used to discard something: Never mind me, I'm leaving. I don't see how it would fit in here at all.
    – terdon
    Commented Mar 3, 2016 at 18:00
  • However it's listed as a synonym by webster. merriam-webster.com/thesaurus/let%20alone
    – Pacerier
    Commented Mar 3, 2016 at 18:54
  • @terdon Not true. Merriam Webster: with this knee I can hardly walk, never mind run; Oxford: he found it hard to think, never mind talk. In this sense it seems to be an exact synonym of let alone.
    – Daniel
    Commented Nov 17, 2018 at 18:15
  • @daniel I mention neither of those in my answer, what do you mean?
    – terdon
    Commented Nov 17, 2018 at 21:09

These are all Constructions.
They have semantic properties, syntactic peculiarities, pragmatic uses, metaphoric sources,
and plenty of idiomaticity to go around.

Luckily, 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).

This doesn't explain the differences with the other ones,
but it does give you an idea how complex the subject can get.

  • Thank you very much. Since I am also questing after the meaning and structure of still/much/even less, would there be references or sources on them too? I upvoted.
    – user50720
    Commented Aug 29, 2013 at 1:27

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