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Concourse 2

Idiomaticity

Idiomaticity is variously defined and described.  The following attempts to single out the two main features of what constitutes and idiom in a language and then to investigate how variable the features are.
You can work through the guide from here or use this menu to go to a part which interests you from this menu.

Definitions Collocation vs. idiom Lexical chunk vs. idiom Phrasal verb vs. idiom Origins Proverb origins
Fixedness and constraints Opacity Duplex expressions Opacity and fixedness One-word idioms Bi- and tri-nomials
Reduplication Ricochet words Frozen similes Style Pronunciation Teaching idioms
At the end of each section, you can click on -top- to return to this menu, simply read on, scroll back or bookmark the page for another time.


What springs to mind when you see these images?  Click here when you have thought of 6 expressions.

bite the bullet ears cake
both ends cat leg pull

There are two important characteristics of the expressions in black.  What are they?
Click here when you have an answer.

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define

Definitions

An early definition of an idiom comes from the linguist and teacher Henry Sweet (a major influence in the Reform Movement's reaction to grammar-translation approaches, incidentally).  He stated:

The meaning of each idiom is an isolated fact which cannot be inferred from the meaning of the words of which the idiom is made up.
(Sweet, 1889:139)

Since Sweet's time, the area has been continually revisited by researchers interested in finding out what constitutes idiomaticity in languages and how the various types of idiom can be classified and analysed.  What we have ended up with is a confusing muddle of terms, definitions and classifications which is, to say the least, unhelpful.  You may, for example, come across any or all of the following terms if you research this area:

figurative idioms or non-compositional metaphors to refer to fact that we can often find a connection between figurative, idiomatic and literal meaning.  It is for example, just possible to figure out what bite the bullet might mean with some knowledge of pre-anaesthetic surgery.  Ditto, perhaps, with have an ace up one's sleeve
binomials to refer to expressions such as time and again, Ladies and Gentlemen which occur as pairs of words, often with a fixed ordering
fixed expressions to refer to idioms which are truly fixed such as an open and shut case
semi-fixed expressions to refer to idioms where some flexibility is allowed.  For example, you can throw in the towel but also throw in the sponge, both meaning surrender, and both derived from boxing
lexicalised expressions to indicate that the expression functions as a single lexeme.  For example, kick the bucket actually just functions as the verb die
opaque expressions emphasising the fact that is often not possible to work out metaphoric meaning from literal meaning as it is with figurative metaphors.  For example, chew the fat
frozen collocations emphasising the fixedness characteristic of some idioms such as a can of worms
restricted collocations referring to those which allow some flexibility but only within a limited range.  For example, you can be a big/large/huge fish in a small/little/tiny pond
semi-idioms to refer to anything which seems like an idiom, insofar as it acts like a single word, but is not completely opaque and fixed.  One part of the expression has a figurative meaning not found elsewhere but the other part is 'normal' as in expressions such as pay attention or foot the bill

It is not the suggestion here that such refinements are useless or deliberately confusing but we are interested in classifications which will be useful to us as English-language teachers rather than research linguists so this guide will focus on two the central characteristics of idiomatic language: fixedness and opacity (or non-compositionality, if you prefer).
This will be at the expense of some precision so if you are looking for more, there are references at the end to on-line, more scholarly articles that you may want to read.
In some analyses, the definition of an idiom includes both fixedness (the inability to change any of the components) and opacity (non-compositionality) but both these phenomena exist on a scale from fully fixed and opaque through semi-fixed and opaque to variable and easily understood.  The definition soon breaks down.


blur

Idiom, collocation, lexical chunks and, phrasal verbs: a blurred area

There are three areas in which the distinction between idioms in the true sense and other word combinations is not distinct.
In some analyses, the definition of idiom is so broad as to encompass most of the language.  For the sake of sanity, the following are not considered here as representing true idioms.
They have their own guides on this site which you will find linked in the list of related guides at the end.

1

Collocations

In the list above, we have something called semi-idioms and the examples are pay attention and foot the bill in which only one part of the expression is used figuratively.
There is a range of verbs which act in this way, collocating with nouns in predictable and fixed patterns.  For example:
    find fault
    lose confidence
    make arrangements
    pay a compliment
    take notice
    win respect
    make an excuse
    do justice
    lend a hand
    gain admiration

and, although the verbs will collocate with a range of other nouns, in these meanings there is usually only one possible choice.  We cannot, for example have:
    *say excuses
    *do arrangements
    *borrow a hand
    *discover fault

etc.
Some of the combinations do allow a certain flexibility so it is possible to have:
    win admiration
    gain, achieve
or earn respect
These items are semi-idioms insofar as only one feature of the definition of an idiom applies.  The verb in such expressions is often described as delexicalised although in some the verb's usual meaning plays a minor role.
Because the nouns are usually transparent in meaning, they are not particularly opaque and the meaning can be derived from understanding their components.  In that sense they are not true idioms.
It is also the case that some verbs may be considered only semi-delexicalised in that their meaning does contribute something to the overall meaning of the clause in which they appear.  For example, in:
    pay a compliment
    take an interest
    set an example
    catch a name
there is some sense of the verb's usual meaning in the clause but it is still very hard to predict which verb will form an acceptable collocation so the expressions may be considered idiomatic in that respect.
They are, however, more or less fixed as we saw and in that respect they are idioms.
For a list of semi- and fully delexicalised verbs, click here.
There is also a lesson for B1 / B2-level learners on delexicalised verbs here (new tab).

We also encountered what some people call frozen collocations which are so strong that they act as single words, always appearing in combination.  The example was a can of worms but many partitives are restricted in their collocations and we also find, e.g.:
    a rasher of bacon
    a pane of glass
    a gust of wind

and so on which can only occur in the context of the commodity or substance they describe.  For more, see the guide to classifiers and partitives, linked below.
Other very strong collocations which are produced and understood as single concepts and not constructed from their component parts include, for example:
    vested interests
    rock solid
    special pleading
    heart rending

and so on.
Whether such expressions are considered idioms (because they are clearly idiomatic) or just very strong collocations is a matter of taste and authorities differ.
When the collocation is noun + noun, some will shade into compound nouns so, for example:
    light bulb
    tree surgeon
    garden rake
    baby sitter

are all analysable as compound nouns and may even be written as one word.
In that sense they are not idioms because it is a simple matter, usually, to add meaning one to meaning two and arrive at the meaning of the whole expression.

2

Lexical chunks

We owe the term lexical chunk to Lewis (1993) and his investigation of a lexical approach to teaching.  He suggests that there is a range of more or less fixed chunks in the language including:

Lewis also focuses on the fact that some verbs, as we saw above, take their meaning from the noun with which they form a strong collocation.  This is what he calls delexicalisation and it mostly affects:
do | have | get | go | make | put | set | take
although we can add other marginal cases such as earn, pay, run and save.
All such multiple-word units (or MWUs in the trade) certainly exhibit some fixedness and are probably produced and understood as single items but they are not opaque in meaning.  They are idioms in the first sense but not in the second.
You may, incidentally, also find such chunks described as holophrases, prefabricated routines or formulas.

3

Phrasal verbs

One definition of a phrasal verb is that the adverb particle combines with the verb to produce a meaning which cannot be retrieved from understanding the sense of the adverb and the sense of the verb: a third meaning needs to be discovered.
Clearly, for example:
    sit back
    sit down
    sit up
    sit in
    sit out

are all verbs post-modified by an adverb but the meaning is extractable by understanding both parts so they are not phrasal verbs or idioms.  Changing the adverb has no effect on the meaning of the verb at all.
However,
    sit by (fail to take action)
    sit on (suppress)
    sit around (be idle)
    sit up (take notice)
are not easily understood by understanding their elements so count as idiomatic because they are both fixed (in the senses used) and opaque.  In this case, changing the particle will affect the meaning of the verb because it is the combination which supplies the third meaning.
Again, of course, there are degrees of opacity, but not of fixedness, because it is possible to understand the meaning of many by a small leap of imagination from the usual meaning of the prepositional use of the particles.  For example, once one has grasped that one of the meanings of out is clear or loud then combinations such as:
    speak out
    shout out
    make out
and more are quite easily understood as are:
    get on
    go on
    move on
    walk on

once we understand that one of the meaning of on is make progress.
Opacity is consequently low.
Phrasal verbs have their own section on this site (as part of the consideration of multi-word verbs in general) so will not feature in this guide to idiomaticity.  See the link at the end for more.

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source

Origins

Although this distinction is not necessary for teaching purposes, it is sometimes helpful in terms of memorisation to know the origin of the idiom one encounters.  There are two possible sources (which often overlap):

  1. Fixed metaphor
    Frequently, very influential texts in English, such as the bible, Shakespeare's works and others, contain metaphors which have come into everyday use and become fixed idioms.  Some metaphorical uses are obscure in origin.  Examples include:
        heart of gold
        laughing stock
        wild goose chase
        wear your heart on your sleeve
        a foregone conclusion
        be cruel to be kind
        salad days
        cold comfort
        a tower of strength

    (all from Shakespeare)
        at the eleventh hour
        by the skin of your teeth
        a millstone around your neck
        the writing on the wall

    (all biblical)
        it gives me the creeps
        go on the rampage

    (both from Charles Dickens)
        spill the beans
        straight from the horse's mouth
        let the cat out of the bag
        count your chickens before they are hatched
        out to lunch
        just my cup of tea

    (all obscure in origin but some may conveniently but speculatively be derived from some occupations)
  2. Historical and specific register origins
    Other idioms derive from certain registers: sport, the military, trade, sailing and so on and are often opaque without a certain amount of knowledge of the history of the domains.  They are usually not completely opaque, however.
    Examples include:
        a sticky wicket (from cricket)
        cover all the bases (baseball)
        run with the ball (rugby or American football)
        game, set and match (tennis)
        a level playing field (many sports)
        plant a seed (horticulture)
        plough through (farming)
        cut a deal (obscure but possibly from card games)
        hit a snag (angling or river navigation)
        a loose cannon (from naval warfare)
        flash in the pan (musketry)
        close ranks (army parade term)
        half-baked (cookery)
        cut and dried (herbalism)
        sail close to the wind (sailing)

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dog

Proverb origins

Let sleeping dogs lie  

Many idioms derive from proverbs in English although they are often truncated because the proverb is well known and does not need to be said in full for the message to be clear.
Such expressions are almost always very opaque because one needs access to the whole idiom to understand the meaning.  Examples include:

Abbreviated idiom Source proverb Meaning
Don't blame your tools A bad workman always blames his tools Poor workers will never blame themselves
Well, we have a bird in the hand  A bird in the hand is worth two in the bush Be satisfied with what you have secured
He's the weakest link A chain is only as strong as its weakest link One weak element will make the whole thing weak
You are clutching at straws A drowning man will clutch at a straw When in desperation we will look anywhere for help
She won't change her spots A leopard cannot change its spots People are reluctant or unable to change their behaviours
All's well that ends well Usually quoted in full If the result is good, past problems don't matter
All that glitters All that glitters is not gold Things may appear better and more valuable than they really are
He's an empty vessel An empty vessel makes the most noise Ignorant people are often the most talkative
A stitch in time A stitch in time saves nine Repair something before it gets worse
He's a bit of a rolling stone A rolling stone gathers no moss People who move between places and jobs don't get rich
It's in the eye of the beholder Beauty is in the eye of the beholder Attractiveness is a personal opinion not reality
Beggars can't be choosers Usually quoted in full If you get something free, you can't complain about the quality
Better late than never Usually quoted in full As long as it's what you want, lateness doesn't matter
Curiosity killed the cat Usually quoted in full Do not pry
It's all coming home to roost Curses, like chickens, come home to roost The consequences of your actions will come eventually
Pearls before swine Do not cast pearls before swine Do not give people better than they can appreciate
We'll cross that bridge later Do not cross the bridge till you come to it Do not waste time worrying about a future that may not happen
Don't kill the goose Don't kill the goose that lays the golden eggs Don't destroy something that is successful
That's the silver lining Every cloud has a silver lining Even bad situations have some good in them
That's just spilt milk Do not cry over spilt milk Don't worry about misfortune which cannot be changed
Make hay Make hay while the sun shines Take advantage of good conditions while they are here
Once bitten Once bitten, twice shy People will not repeat actions which were unpleasant
The grass is always greener The grass is greener on the other side of the fence People always want more than they have
We don't want too many cooks Too many cooks spoil the broth Having too many people in a team confuses a task
When in Rome When in Rome, do as the Romans do Adjust your behaviour to suit the culture you are in
You can lead a horse to water You can lead a horse to water but you can't make it drink You can show people how to do something but you cannot force them to do it
That's the last straw It's the last straw that breaks the camel's back A small increment can destroy all of something
Many hands Many hands make light work The more people you have the easier a job will be
You're an early bird It's the early bird which catches the worm The sooner you start the better will be the prospects

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fixed

Fixedness

This is not an on-off characteristic.  Some idioms are more fixed than others, some are very flexible.  Here's a cline for you to see what's meant.  Where would you put the idioms on right in the cline on the left (if idioms they actually are)?  Click on the image for some comments when you have an answer.

fixedness cline through thick and thin
hammer and sickle
aid and abet
have a blast
hit the sack
off one's rocker
call it a day
assets and liabilities
left, right and centre
life or death
back to the drawing board
cut corners
put all your eggs in one basket
torrential rain
wouldn't be caught dead
miss the boat
make the grade
make the beds
raining cats and dogs

There is an interesting exception to fixedness.
Some idioms and even binomials which are normally considered wholly fixed can be modified with intensifiers.  It is possible, therefore, to have:
    I have been rushing
hither and bloody yon all day
    I
smell an extremely large rat
    I've
missed the damn/an important boat
    have a total/absolute/complete blast
etc.  In particular, the so-called taboo words, bloody, bleeding, damn etc., are used in this way.

flexible

Flexibility

Idioms may be flexible to a certain extent, then, but the flexibility is also analysable by type.

  1. Conjugation
    Idioms which contain verbs are frequently conjugated to conform to the normal rules so, e.g.:
        pass the buck
    may be
        passes, passed, is passing the buck
    and so on and the verb can be nominalised as in:
        I resent your passing the buck
    Pronouns will change in the normal way and may be accompanied by other changes, e.g.:
        She bit off more than she could chew
        He has bitten off more than anyone could chew
  2. Passivisation
    Such idioms can also be made passive so we can allow
        They have cooked the books
    and
        The books have been cooked
  3. Insertion of words (usually adjectives or adverbs)
        right at the eleventh hour
        teaching new tricks to a very old dog
        by the absolute skin of my teeth
  4. Re-formulation
        We need a level playing field → We need to level the playing field
        She has a heart of gold → Her heart is of pure gold
police

Constraints

Some idioms are constrained structurally.  For example:

  1. Some can only be used in the negative so we allow:
        I didn't sleep a wink
        I can't make head (n)or tail of it
        She wouldn't be caught dead with him

    but not:
        I slept a wink
        I made head or tail of it
        She would be caught dead with him
  2. Some can only appear in the passive or active voice so we allow:
        He's fed up with the work
        I am snowed under with emails
        Don't beat about the bush
        Let's call it a day

    but not:
        *The work fed him up
        *The emails snowed me under
        *The bush was beaten about
        *It was called a day

    However, reformulation is often allowed so we see and hear:
        He missed the boat
        The boat was missed
        I gave him the benefit of the doubt
        He was given the benefit of the doubt
        The benefit of the doubt was given to him
        She was let off the hook
        They let her off the hook

    and so on.
    This is a wholly unpredictable area.

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opaque

Opacity or non-compositionality

Again, there's a cline because there are levels of opacity and transparency.  The image below separates them into those whose meaning is obvious (literal), those where it can be deduced (figurative uses) and those which are wholly opaque.
As you did above, locate these expressions on the right somewhere on the cline on the left and then click the image for a commentary.

transparency  barking up the wrong tree
a bitter pill to swallow
by the skin of one's teeth
bread and circuses
kiss and tell
heads or tails
spick and span
holding all the aces
at a snail’s pace
a dime a dozen
bite off more than one can chew
cut the mustard
bob and weave
under the weather
hot and bothered
research and development
come rain or shine
Tom, Dick and Harry

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double

Duplex expressions

Most strong collocations are perfectly easily understood by understanding the individual lexemes.
For example, there is no difficulty at all in understanding
    counterfeit money
    bank account
    garden party
    make a choice
    deeply regret
    wholly unacceptable

and thousands more by understanding the words in them, even when, as in the fourth case, the verb carries little real meaning.

There are, however, some collocations which may be literal in meaning in one sense and used figuratively in another.  For example:
    a fine-tooth comb
may be reference to a particular type of comb which has small gaps between the teeth.  However, when we say:
    They went through the accounts with a fine-tooth comb
we are referring to very careful examination and not to a comb at all.  Equally,
    a slippery slope
may simply refer to an ice-like surface on an incline but in something like:
    She's on a slippery slope to being dismissed
we are referring to the fact that small actions or omissions can result in large, negative consequences.
Furthermore, some idiomatic expressions which look like simple collocations are, in fact, only used figuratively so, for example:
    He's a big noise in the army
refers to someone who is important and influential but the words big and noise do not elsewhere form a natural collocation (the preferred adjectives being, loud, huge, deafening etc.)

Macis and Schmitt (2017) estimate that a quarter of strong collocations have figurative (i.e., idiomatic) meanings and are, therefore, more sensibly dealt with in the classroom as idioms which should be learned and produced as single lexical chunks.
Looking out for collocations which are, in fact, being used figuratively and idiomatically may pay dividends in terms of teaching and remembering lexis.

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relationship

The relationship between fixedness and opacity

There is a tendency for these two characteristics to rise and fall together.  In other words, the more fixed and inflexible the expression, the more likely it is to be opaque in meaning and vice versa.

We can find low fixedness with some expressions but they are likely to be quite literal in meaning.  For example, as old as ... can be followed by a number of expressions (God, the hills, Noah etc.) but opacity is also low.
Similarly, strong collocations such as a pronounced accent are not firmly fixed (we can have strong, broad etc. as the adjective with roughly the same meaning) but they are usually easy to understand (if not to learn).

On the other hand, an expression such as off one's rocker has quite high fixedness (there's only one conventional alternative to rocker, trolley) and it is also quite high in opacity.  Extreme cases of fixedness are also, often, extreme cases of opacity.  Expressions such as let the cat out of the bag are both opaque and fixed as are binomials such as helter-skelter.

There are, nevertheless, instances, especially with binomials, of low opacity and high fixedness.  In other words, they always occur together and in the same order but are straightforward to understand.  Examples are:
    here and there
    hand in hand
    dead and buried
etc.

The moral?
Whenever we find a highly opaque expression, the way to bet is that it is also firmly fixed.  The reverse is not always true.
Here's a graphical representation of that.  Before teaching idioms, it is worth 5 minutes of the planning time to consider where in the matrix the target language items fall.
matrix

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1

One-word idioms

Idioms are usually understood to be phrases or clauses which cannot be immediately understood by retrieving the meaning of the words in them.  However, many words, especially verbs, are or can be used metaphorically and qualify as idioms because they are (obviously) fixed with synonyms rarely having the same effect and they are often quite opaque in meaning.
Some examples are:
    The show bombed
    I was bombarded with questions
    The question threw me
    They sacked him
    You have lost me
    It's a pig
    My printer died

etc.
None of these examples will mean the same when synonyms or near synonyms are used so, for example:
    The show shelled
    I was blasted with questions
    The question flung me
    They plundered him
    You have misplaced me
    It's a hog
    My printer perished

are all either incomprehensible or extremely unnatural.

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parrots three

Binomials and trinomials

Because these are so common in English, they merit a short section to themselves.  Many of these items are worth teaching as single lexemes because they are handy language chunks, they are extremely common and they are not easily paraphrased.
There are some general characteristics of binomial expressions:

  1. They consist of two lexical items belonging to the same word class so they are, noun + noun, verb + verb, adjective + adjective, adverb + adverb.  Examples of the four main sorts are:
        He has lived here man and boy
        You can take it or leave it
        And that's the truth, pure and simple
        I will do it
    sooner or later
    (Rarely, the two items are not of the same word class but follow similar structural forms so, for example:
        We were home and dry
    in which home is an adverb and dry an adjective but both are joined to the subject by the copular verb.  That is probably not something with which to trouble your learners.)
  2. Some are literal (apples and oranges etc.), some are figurative (the chicken or the egg etc.) and some are wholly opaque (milk and honey etc.).
  3. Some, such as helter-skelter, super-duper etc., contain words found nowhere else.
  4. When two nouns are joined, the resulting expression is often singular, e.g.:
        Fire and brimstone is all he shouts about
        Thunder and lightning is on its way
    but, if the nouns are already plural, that is not the case:
        His eyes and ears are everywhere
        The stars and stripes are flying over The White House
  5. The order of the items is usually fixed although with some, reversal has no effect.  We can have:
        She worked day and night
    and
        She worked night and day
    We allow
        I'll do it sooner or later
    but not
        *I'll do it later or sooner
  6. The tenses and numbers of items are normally retained in both items so we get, for example:
        It's done and dusted
        It comes with many bells and whistles
        I'll name and shame him
        There will be some naming and shaming
        They were named and shamed
    etc. and:
        *for all intent and purpose
        *It's time to cut and be running

    are not encountered.
  7. The items are frequently joined with the coordinator and but there are other possibilities including: but, or, either ... or, neither ... nor, to, after, by, in.
  8. Often the items rhyme or are, more often, alliterative as in, e.g.:
        make or break
        high and dry
        house and home
        do or die

    etc.
    In some, a phenomenon called assonance is discernible so for example, a stressed vowel will be the same in both items or a consonant duplicated with different vowels as in harum scarum or tittle-tattle.
  9. Because binomials operate as single lexemes, they are subject to the collocational forces as all other lexemes so, for example:
        high and dry collocates strongly with the verb leave
        high and low collocates with verbs such as look (for), search, hunt and seek
        dead and buried collocates with nouns such as ideas, proposals, suggestions, schemes and plans
    and so on.
  10. Binomials often intensify, especially reduplicative ones, so, e.g.:
        She went from strength to strength
    Ones in which the two items are synonyms have the same effect:
        He's at my beck and call
    and, perversely, antonym pairs also intensify:
        We searched high and low, in and out, in each and every part of the house

Here's a selection.
Fuller lists with some doubtful inclusions are available via a web search.

joined with coordinators (and or or/neither ... nor etc.)

above and beyond
airs and graces
alive and kicking
all or nothing
an arm and a leg
apples and oranges
assault and battery
back and forth
ball and chain
beck and call
beer and skittles
bells and whistles
for better or worse
bits and bobs
bow and arrow
by and large
cat and mouse
the chicken or the egg
cut and dried
cut and run
day or night
dead and buried
dead or alive
divide and conquer
do or die
down and out
each and every
eyes and ears
far and wide
horse and carriage
intents and purposes
kill or cure
kill or be killed
knife and fork
law and order
love nor money
lo and behold
loud and clear
make or break
man and boy
milk and honey
more or less
neat and tidy
nip and tuck
nook and cranny
fast and loose
fingers and thumbs
fire and brimstone
first and foremost
forever and a day
free and clear
fight or flight
(neither) fish nor fowl
fun and games
(come) hell or high water
(neither) here nor there
hit or miss
hale and hearty
hard and fast
hearts and minds
here and now
high and dry
high and low
home and dry
hope and pray
nuts and bolts
odds and ends
pure and simple
pepper and salt (hair colour)
rags to riches
rain or shine
research and development
room and board
sink or swim
sooner or later
take it or leave it
salt and pepper (seasoning)
seek and destroy
short and / but sweet
sick and tired
slash and burn
smash and grab
snakes and ladders
stand and deliver
supply and demand
sweetness and light
tables and chairs
tar and feather
tea and crumpets
thunder and lightning
time after time
to and fro
tooth and nail
touch and go
trial and error
up and about
vim and vigour
wait and see
wine and roses

with reduplication
The term reduplicate is a slight misnomer because the words are duplicated, not reduplicated.

again and again
all in all
around and around
arm in arm
back to back
bit by bit
bumper to bumper
by and by
cheek to cheek
closer and closer
coast to coast
day to/ by day
elbow to elbow
end to end
dog eat dog
from ear to ear
an eye for an eye
eye to eye
face to face
hand in hand
head to head
heart to heart
higher and higher
horror of horrors
less and less
little by little
lower and lower
man to man
more and more
mouth to mouth
neck and neck
never say never
nose to nose
on and on
one by one
out and out
over and over
round and round
shoulder to shoulder
side to side
step by step
strength to strength
through and through
time after time
(from) time to time
two by two
toe to toe
up and up
wall to wall
for weeks and weeks
woman to woman

with rhymes or similar sounds
These are often considered a subset of reduplicate phrases but exactly where the border is between a reduplicative and these examples lies is not always easy to determine.  Parts of the words are clearly duplicated and the words often rhyme, a phenomenon encapsulated in the alternative name, ricochet words.
The use or not of a hyphen is often idiosyncratic to the writer as is whether some are written as one word.

belt and braces
box and cox
chalk and talk
chit-chat
dilly-dally
ding-dong
double trouble
even Stevens
fender-bender
flim-flam
flip-flop
hanky-panky
harum-scarum
helter-skelter
higgelty-piggelty
high and dry
hire and fire
hither and thither
hocus-pocus
hodge-podge
hoity-toity
horses for courses
hubble-bubble
huff and puff
hurly-burly
hustle and bustle
meet and greet
mish-mash
namby-pamby
name and shame
near and dear
nitty-gritty
odds and sods
out and about
pell-mell
ping-pong
pitter-patter
razzle-dazzle
riff-raff
roly-poly
shilly-shally
time and tide
tip-top
tittle-tattle
town and gown
use it or lose it
wear and tear
willy-nilly
wine and dine
wishy-washy
yea or nay
There are, obscurely, rules for which item is placed first when the vowel sounds differ and they have to do with what is called ablaut reduplication.  Ablaut describes the alternation in vowels that we see in, e.g., sing, sang, sung or ring, rang, rung and so on.
Although there are very rare exceptions, the rule is that the first item contains a higher vowel than the second.  That is to say, the tongue is higher in the mouth when the vowel in the first item is produced than in the second.
High vowels in English include: /ɪ/ as in kid, /iː/ as in heel, /ʊ/ as in foot and /uː/ as in shoe.
Low vowels include /æ/ as in hat, /ɒ/ as in wash, /ʌ/ as in cup, /ɔː/ as in taught and /ɑː/ as in car.
So it is that we get shilly-shally, not shally-shilly, ping pong, not pong ping, chit-chat not chat-chit, ding-dong not dong ding, flim-flam and flip-flop not flam-flim and flop-flip and so on.
It also explains why most speakers will say this and that not that and this and so on.
This phenomenon is rarer for trinomials in the list below but is evident in, e.g., cool, calm and collected, eat, drink and be merry and this, that and the other.
This appears to be non-language specific, incidentally.

Some quite common words in English are derived by reducing rhyming or similar-sounding binomials so, e.g.:
    patter
is a reduction of pat-pat (to hit gently).
    blabber is a reduction of blab-blab
    paddle is a reduction of pad-pad
and so on.
The technical term for this phenomenon is that the word is a frequentative.

trinomials

There are fewer of these and they almost always employ and as the coordinator.  Examples include:

beg, borrow or steal
blood, sweat and tears
cool, calm and collected
eat, drink, and be merry
ear, nose and throat
gold, silver, and bronze
guns, germs, and steel
healthy, wealthy, and wise
here, there and everywhere
hook, line and sinker
hop, skip and jump
judge, jury and executioner
left, right and centre
lights, music, action
lock, stock and barrel
nasty, brutish and short
planes, trains, and automobiles
ready, willing and able
reading, writing and arithmetic
red, white and blue
sex, drugs, and rock 'n' roll
tall, dark and handsome
Tom, Dick and / or Harry
shake, rattle and roll
this, that, and the other
way, shape, or form
win, lose, or draw

hyphenation

Many binomials, especially those without a connecting conjunction, are conventionally hyphenated so we get helter-skelter, willy-nilly, harum-scarum and so on.
Others are only hyphenated when they are used adjectivally so we get, for example:
    It's a question of law and order
    The price is subject to the influence of supply and demand

etc., because these are being used as nouns, but we have:
    This is a law-and-order issue
    It's a supply-and-demand influence

etc., because these are adjectival uses.
Trinomials exhibit the same phenomenon.

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bolt

Frozen or fixed similes

Similes explicitly compare two items, usually, in English, with the as ... as formulation.
A number of these constitute a kind of idiom although in almost all cases they are a) fixed and b) often (but not always) quite literal and transparent in meaning.  To extract the meaning, one has usually only to understand the first item and then understand that the idiom emphasises its strength.
They include items such as:

as blind as a bat
as black as night
as clean as a whistle
as cool as a cucumber
as dead as a doornail
as fit as a fiddle
as flat as a pancake
as free as a bird
as fresh as a daisy
as good as gold
as hard as nails
as keen as mustard
as large as life
as light as a feather
as mad as a hatter
as old as the hills
as plain as day
as quiet as a mouse
as regular as clockwork
as right as rain
as safe as houses
as sick as a dog / cat
as strong as an ox
as stubborn as a mule
as thin as a rake

etc.
Such expressions, too, are often alliterative.
The main elements are usually given equal stress.

A secondary form for these fixed expressions employs the like preposition.  These are not adjectival, so often it is a noun being compared to another or a verb being used figuratively as in

eyes like a hawk
a face like a brick wall
a hand like a bunch of bananas
drink like a fish
smoke like a chimney
fight like cat and dog
eat like a horse
eat like a bird
run like clockwork
cry like a baby
spin like a top
work like a Trojan
be like a child in a sweet shop
be like a bull in a china shop
be like a dog with two tails
be like a headless chicken
be like watching paint dry
go like a flash of lightning / the wind

They are almost totally confined to informal speech and writing.  Such clichés are often disparaged in more formal texts.

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style

Style and register

Most idiomatic language is stylistically informal and inappropriate in a number of situations.  Idioms are used extensively in informal speech and writing (especially in newspapers), however, so a knowledge of common ones is very helpful for learners of English.  Unfortunately, there are, by some estimates, 25,000 of them in English.
In more formal contexts, idioms will often be avoided so we are unlikely to find, for example:
    Buckingham Palace announced that the Queen is under the weather
    The government negotiators are reluctant to open a can of worms, said the White House spokesman.
etc.
Learners of the language can be tempted to overuse idiomatic language in situations where it is not appropriate or they can get the meaning just slightly wrong and produce, e.g.:
    *I'll do it willy-nilly
    *I'm down in the dumps with her
    *The government isn't cutting the mustard for it

In common with many idiomatic expressions, bi- and trinomials are often informal and common in spoken language.
A few, however, such as first and foremost, more and more, intents and purposes and others are encountered in formal writing and some are confined to specific registers such as economics (supply and demand), the law (aid and abet), education (reading, writing and arithmetic) or engineering, politics and commerce (research and development, wear and tear, trial and error, ways and means).
They are, to some extent, clichés and accordingly much used in journalese.

The same considerations of grammar and form apply here as they do in the teaching of any lexis.
It is important to make sure, then, that idiom presentation is set in an appropriate context (both style and register) and that word class is considered along with aspects of transitivity, complementation and so on.

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pronounce

Pronunciation

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teaching

Teaching idiomatic language

Too often, in coursebooks and study guides, idioms and idiomatic language are relegated to peripheral 'Useful phrases' boxes and then ignored.  That's a great pity as it is almost impossible to become fluent in English without acquiring a fair number of idiomatic expressions.  In fact:

Most students are very interested in learning idiomatic language.  They recognize it as an area in which they have difficulties, and appreciate systematic instruction.
(Irujo, 1986: 242)

There's nothing mysterious about this.  We have to make the same judgements that we make when teaching lexis of any sort.  In other words, we must consider appropriacy and style, range, learnability, frequency and so on.  For more, see the guide to teaching lexis, linked below.

difficult

Difficulties

Idioms present some serious difficulties for learners and that is one reason that they have fallen out of fashion of late.

  1. Idioms date quite rapidly.
    It may be the case that native speakers of English used to exclaim
        Ye Gods and little fishes!
    when astonished by something but to do so now would make the speaker sound very odd and old fashioned.
    The popular example of dating is the expression
        raining cats and dogs
    which almost no native speaker would use but which is often heard from learners of English.  Other examples of dated idioms to avoid include:
        to be in seventh heaven
        to keep up with the Joneses
        the gift of the gab
        to be dead beat
        to take a rise out of someone
    and there are many more with which it is unwise to burden learners.
  2. Idioms require learning and reproducing a string of words exactly.
    Some idioms are quite long strings and impose something of a strain on the memory.  For example:
        choose the lesser of the two evils
        give someone the benefit of the doubt
        cross that bridge when you come to it
    are all quite long and hard to remember as language chunks.
  3. Fixedness and naturalness.
    Getting even one word wrong in an idiom can often result in the expression sounding absurd and unnatural, although it will rarely be misunderstood.  For example:
        *That's a sour pill to swallow
        *I wash my hands from it
        *Speak of a devil
        *It's not rocket physics
    are all wrong by one word and even missing or misusing an article can make the speaker sound foreign or amusing.
  4. Some idioms are stand-alone expressions but some can only be used embedded in co-text.  For example:
        Get your act together
        Better late than never
        So far so good
        You can say that again
    are all routinely used as isolated phrases (although they can be embedded in other language).
    However:
        the best of both worlds
        miss the boat
        beat around the bush
        on the ball
        in the mire
    are only used when they are embedded in other language and cannot stand alone.
files

Classification and selection for teaching

One can, of course, teach idioms only as and when they arise in texts used in the classroom or in response to learner enquiries.  That makes some sense because it avoids problematising the issue and demystifies a complicated area.
However, especially at more advanced levels, many learners appreciate that they can only sound truly natural in English if they are able to use a reasonably wide range of idiomatic expressions.  They will often, therefore, appreciate and be motivated by lessons which focus specifically on idioms and idiomatic language.
The teacher's problem is how to select, group and present the most common ones.  There are three main ways:

  1. A shared base word or conceptual category:
    It has been noted that some words in English feature in idioms more than most and provide a jumping-off point as well as a conceptual hook to help people remember the expressions.  For example:
    colours
        be green with envy
        have green fingers
        give the green light
        a red-letter day
        to be in the red
        catch red handed
        red tape
        red carpet
        see red
        red blooded
        black out
        black and white
        black and blue
        black market
        black looks
    verbs / nouns
        bite the bullet
        bite off more than you can chew
        her bark is worse than her bite
        grab a quick bite
        bite your tongue
        throw a party
        throw someone (puzzle or confuse)
        throw a wobbly
        throw the toys out of the pram
        throw your hat in the ring
        catch someone (meet)
        catch a programme
        catch it (be punished)
        there's a catch
        catch / get a joke
    body parts
        head for home
        head in the clouds
        a head start
        head over heels
        over my head
        see eye to eye
        keep an eye on
        give your eye teeth for
        by the skin of your teeth
        have a sweet tooth
        get your teeth into something
        have / get cold feet
        foot the bill
        put your foot in it
        best foot forward

        footloose and fancy free
        face the music
        face to face
        get in someone's face
        face up to something
        elbow in
        let your hair down
        play by ear
        be neck and neck
        shoulder responsibility
        bend the knee
        have a knees up
        toe the line
        cost an arm and a leg

    etc.
    animals
        a fly on the wall
        a fly in the ointment
        wouldn't hurt a fly
        do the donkey work
        flog a dead horse
        the lion's share
        keep the wolf from the door
        dog tired
        let sleeping dogs lie
        let the cat out of the bag
        smell a rat
        a wild goose chase
        up with the lark
        a fish out of water
        a cold fish
  2. A shared source
    We saw above that many idioms derive from professions and activities and this too can be a way of helping the memory.  For example:
    From sports and leisure activities
        the ball is in your court
        off his own bat
        call the shots
        down to the wire
        be blinkered
        to spur on
        to give a free rein
        to keep on a tight rein
        a front runner
        jump the gun
        the home stretch
        hold your horses
        be in the saddle

    and hundreds more.
    From warfare
        the big guns
        get your head over the parapet
        a war of nerves
        a war of words
        to be in the wars
        have a blitz
        bombard with questions
        take no prisoners
        rank and file
        to steal a march
    From commerce and business
        the bottom line
        rig the market
        insider information
        have a monopoly
        get down to business
        do the business
    From seafaring
        learn the ropes
        clear the decks
        a broadside
        fly the flag
        toe the line
        brass monkeys
        sail before the wind
        be taken aback
  3. A shared function
    Idioms can be classified by the sorts of things they refer to and this is also a useful way of helping the memory.  For example:
    Describing personality
        a pain in the neck
        a dark horse
        a bright spark
        a wet blanket
        a rough diamond
        the life and soul
    Complementing
        She's a diamond
        You're a trooper
        You're a brick
        He's a class act
        It's worth an Oscar
    Complaining
        breathe down someone's neck
        Pull your weight
        Get off my back
        pay through the nose
        argue the toss
        have a bone to pick
        make a mountain out of a molehill
apple

Techniques and classroom approaches

Idioms and idiomatic language have some characteristics that make certain approaches more worthwhile and productive.

More teaching ideas can be found in Irujo (1986)

In the section for learners on this site, there are some exercises to do with idioms and binomials.  Check the exercise index under vocabulary for more.


There is a very short test on some terms to help you recall all this.



Related guides
synonymy for more on how this and related areas work with more on similes and metaphors (fixed and otherwise)
semantics for a theoretical guide to meaning
teaching lexis for some practical ideas
the lexical approach for a guide to an approach to analysing and teaching language which focuses on chunks, holophrases, polywords and more
collocation for more on this form lexical relationship
classifiers and partitives for a guide which considers the role of restricted partitives such as pane of and rasher of
empty or delexicalised verbs for a list in PDF format
multi-word verbs for the guide to many idiomatic expressions


References:
Barkema, H, 1996, Idiomaticity and terminology: a multi-dimensional descriptive model, Blackwell Publishing Ltd., Studia Linguistica, Volume 50, Issue 2, pp. 125-160
Benor, SB & Levy, R, no date, The Chicken or the Egg? A Probabilistic Analysis of English Binomials, available from http://www.pdfmanuale.com/file/9GW/the-chicken-or-the-egg-a-probabilistic-analysis-of-english.html [accessed January 2015]
lrujo, S, 1986, A piece of cake: learning and teaching idioms, English Language Teaching Journal, 40 (3) pp. 236-242, Oxford: Oxford University Press
Lewis, M, 1993, The Lexical Approach, Hove, England: Language Teaching Publications
Macis, M and Schmitt, N, 2017, The figurative and polysemous nature of collocations and their place in ELT, ELT Journal Volume 71/1 pp50-59, Oxford: Oxford University Press
Moreno, REV, no date, Idioms, Transparency and Pragmatic Inference, available from http://www.phon.ucl.ac.uk/publications/WPL/05papers/vega_moreno.pdf [accessed January 2015]
Schmitt, N and McCarthy, M, 1997, Vocabulary: Description, Acquisition and Pedagogy, Cambridge: Cambridge University Press
Sweet, H, 1889, The practical study of languages, London: Oxford University Press (Reprinted in 1964)