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Clausal subordination

subordination

Before tackling this guide, you would be wise to consult the guide to subordination and coordination (new tab) where the differences and similarities between the phenomena of coordination and subordination are analysed.
This guide deals with a number of issues covered in more detail elsewhere such as conditionality and concession.  You can track other guides to the area via the section on syntax: clauses and phrases (new tab).

You will know if you have followed the guide to subordination and coordination that compound-complex sentences with mixtures of various types of coordination and subordination are not uncommon in English.
In what follows, for the sake of clarity, we will deal with single instances of subordination at a time and will not consider coordination at all.

Here's a list of the contents of this guide.
Clicking on -top- at the end of each section will bring you back to this menu.

simple subordinators compound subordinators correlative subordinators marginal subordinators shared structure Function and meaning
causal subordination temporal subordination ordering clauses Alternative subordination Non-finite clauses exclusions
Clause positioning weighting ambiguity right ordering pronouns Pronunciation


subordinator

The subordinators

We can classify subordinators in two ways:

  1. By their structural characteristics – how they are formed and the nature of the surrounding syntax
  2. By what they do – their functions in terms of making meaning

We'll do both.


structure

Structural characteristics

We can divide the structural characteristics into three classes:

Simple subordinators
simple
This is by far the largest class and contains the subordinators that we would consider the essential subordinators in English.  They are all single words and many will be familiar to most learners above A1 level.
Here's a list:
after
although
as
because
before
if
however
lest
once
since
till
unless
until
when(ever)
where(ever)
whence
whereas
whereby
whereupon
while
whilst
whither
Some examples:
After he had driven for 4 hours he stopped for coffee
He couldn't leave until the work was done
Before it rains, we should take the dog out
However you want to do the work is fine with me
I told him it was a stupid idea whereupon he became angry
Whereas I have often worked late, Shirley never does
Once we've finished we can go for a drink
Whereupon, whereby and whither apart from being slightly archaic, can only come before the second clause for semantic reasons (they introduce chronological or spatial ordering of events).
Compound subordinators
compound
These are rarer.  Many insist on being followed by that and some can optionally be followed by that.  Others are followed by as and some are simply rather irregular.
Here's a list:
Obligatory that Optional that Obligatory as Others Some examples:
except that
in order that
in that
*so that
such that
assuming that
considering that
given that
now that
provided that
providing that
seeing that
supposing that
as far as
as long as
as much as
as soon as
insofar as
so long as
as if
as though
in case
rather than
sooner than
He did all the work except that he forgot the painting
Now that he's at university, we can rent out his room
Considering that he's nearly 80 he's very active
Insofar as she could she answered all the questions
Assuming that it's open I can get it at the corner shop
I'd sooner stay in tonight than go to the party
Seeing that it's under guarantee, I don't worry about it
We can finish today given that we are all working on it

The phrase so that is listed here as a subordinator which is the role it performs when we are linking action with purpose as in, for example:
    I covered it well so that it wouldn't get wet
However, the phrase also functions as a coordinator in, for example:
    The fog was very dense so that I couldn't see my way
in which it means so and is only a coordinator expressing consequence.
We can demonstrate this by trying to reverse the clauses so while:
    So that it wouldn't get wet, I covered it well
is acceptable as a sentence containing subordination,
    *So that I couldn't see my way the fog was very dense
is not because coordinators must retain their position between clauses.
Correlative subordinators
correlate
These consist of two parts but are separated by the independent clause.  Here's the (short) list of these with their characteristic function.
Conditional Concessive Proportional Alternative Some examples:
if ... then although ... yet as ... so
more/less ... than
the ... the
whether ... or If you cook then I'll wash up
Although his handwriting is poor yet it can be understood
The more people who come the better it will be
Note that although ... yet is archaic and formal.  The sense is most often simply expressed with although.
The use of then in conditional expressions is not obligatory but it only appears in the second clause.
Marginal subordinators
margin
Some items are actually prepositional in function (and there is a view that all subordinators perform preposition-like functions) but still act to subordinate one clause to another.  Here's a short list:
Temporal Causal Contrastive Concessive Some examples:
every time (that)
the moment (that)
because of
due to
on account of
despite
in spite of
in the light of
regardless of
He complained the moment / every time the manager was available
Due to / on account of / because of not enjoying concerts, he stayed at home
In spite of / despite being warned she went ahead
Regardless of John avoiding the work, it was finished on time
In the light of Anne doing all the groundwork, we can begin
The prepositional nature of these items is revealed by the fact that they can mostly be followed directly by a noun phrase and serve to link it to the verb.  For example:
    Because of the rain, I stayed at home
    In spite of the snow, I took the dog out
    In the light of the new information we need to recalculate the figures

This does not apply to the two temporal subordinators which are not followed directly by noun phrases.
sharing

Shared structural characteristics

All subordinators share certain attributes which distinguish them from coordinators and make them teachable together (but not all of them at once, please).

Clause mobility
It is possible to have, for example,
    I came because I was interested
and
    Because I was interested, I came
and
    Unless you work a bit more, you'll fail the examination
and
    You'll fail the examination unless you work a bit more
and even
    There will, if we work really hard, be time to finish this
Although the emphasis is different, all three orderings are grammatically acceptable.
You cannot do this with coordinating conjunctions, of course, or you get nonsense like:
    *But you weren't at home I telephoned
Subordinators travel with their clause; coordinators are independent of either clause and come between them.
Allowing the addition of other conjunctions
Subordinators can themselves be preceded by coordinators in, for example:
    He didn't come because it was raining and because he was too tired
    You can leave early provided that you have finished but only if the boss says it's OK

Again, coordinators do not allow that so we cannot have, for example:
    *She called you and but you were in a meeting.
Non-ellipsis of the subject
Usually, coordinators allow the ellipsis of the subject providing it is common to both clauses but subordinators do not so we can have
    John came home and cooked
which is a coordinated set of two clauses with ellipsis of the second subject.
Subordination, however, requires the repetition of the subject in both clauses so we allow:
    I came in order that I could see you
and
    I won't drink if I am driving
but not
    *I came in order that could see you
or
    *I won't drink if am driving
Assumed reference
In a sentence with two coordinated clauses such as:
    He was exhausted but John worked on till six
it is averred by some that he and John must refer to different people.  In other words, he cannot be a cataphoric reference to John in a coordinated sentence.  This is somewhat questionable but at best the sentence is ambiguous insofar as he and John could refer to the same person or to different people depending on context and co-text.
With subordination, on the other hand, cataphoric reference is always assumed so in
    Although he was exhausted, John worked on till six
it is inevitable that he and John will be assumed to be the same person unless intonation, stress and context demand that the sentence be understood differently.
Inability to join two equal subordinate clauses
In this part, coordinators in green, subordinators in red.
Coordinators can join two subordinate clauses together as in, e.g.:
    Because I wanted to see you I came to the party and stayed for hours
in which the coordinator and joins two equal-value clauses, but we cannot have:
    *She came when you asked in order that you saw her
because only coordinators can link two subordinate clauses together.
Subordinators can, of course, link a further subordinate clause making a complex tree of subordinations so we can have, e.g.:
    She came to the party because she wanted to talk to him and because she enjoys parties if they are not too large and noisy
Here, we have a main clause:
    She came to the party
a subordinate clause:
    because
she wanted to talk to him
linked to another equal-value subordinate clause:
    and
because she enjoys parties
with its own subordinate conditional clause:
    if
they are not too large and noisy
.
If that seems complicated to access, try a diagram:
complex subordination
Theoretically, there is no limit to the number of clauses which can be linked in this way.  Human cognition, however, limits the number of clauses to a maximum (rarely) of eight.

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function and meaning

Function and meaning

Functionally, there are at least the following classifications.  There are other ways to do this, of course, because people conceptualise things slightly differently.  For teaching purposes, the following will do.  You will notice that some subordinators can perform more than one function so appear in more than one category.  The examples have been deliberately chosen to apply to the less-frequently encountered items.
The categories are slightly different from those in the guide to conjunctions, by the way.

Function Subordinators Examples and notes
conditional as / so long as
even if
if
if ... then
on condition that
provided that
providing that
supposing (that)
unless
If we want to get this done then we'll have to start soon.
Supposing that John doesn't pay, what will happen then?
Unless I am very much mistaken, that's his brother in law.
You can do that just as long as nobody gets hurt.

See the guide to conditional and concessive subordination, linked below, for more.
The unusual nature of unless is covered there, too.
concessive although
although ... yet
*as
as far as
assuming (that)
considering (that)
even though
given (that)
in that
insofar as
presuming (that)
*that
Given that he has no money, I can see no way he will pay you.
Insofar as the work needs doing, I suppose I shall have to pay for it.
I will ask him presuming we meet, of course.
Although she tried her best, yet she failed to pass.
As far as his work is concerned, I have no complaints.

See the guide to conditional and concessive subordination, linked below, for more.
causal / resultative as
because
for fear that
in case
in order that
lest
seeing that
since
so that
such that
whereby
I came early so that I could help out a bit.
He wrote his essay such that the links between its parts were clear.
Seeing that he is unharmed, there's no reason to panic.
In case you need me, I'll be by the phone.

He opened the hatch whereby he could get onto the roof.
These subordinators have some complex and troubling characteristics so get a section to themselves, below.
temporal after
as
as soon as
before
hardly … when
immediately
no sooner … than
now (that)
once
scarcely … when
since
till
until
when
whenever
whereupon
while
whilst
Now that we have finished the work, we can relax.
Once we have finished the work we can relax.
I voiced my objection at the meeting whereupon I was fired.
Whenever I speak to him, he seems distracted and busy.
I cooked whilst my sister did the gardening.

Note that since can also act as a preposition as in, e.g., since the war, since 1959 etc.
The word whereupon is rare and prohibits the re-ordering of the clauses because it signifies the ordering of events.
See the section below for more consideration of these.
exclusive except (that)
lest
rather than
sooner ... than
whether ... or
I would sooner eat on the terrace than be in this smoky restaurant.
He reinforced the floor lest the snooker table be too heavy.
Whether he comes or doesn't come, makes no difference to us.

Because of their nature, subordinate clauses in these cases are often ellipted as in, e.g., It makes no difference whether he comes or no(t).
The subordinator lest is somewhat old fashioned and is generally followed by a clause in the subjunctive (as in the example).
spatial where
wherever
whence
whither
Wherever she looked, she saw enemies.
The pub is over the hill, whither we are going today.
He knew the city, whence he came, really well.

Whence and whither are unusual in modern English and probably not worth troubling any but the most advanced learners with.
The adverb where also functions as a relative adverb (see link below).
comparative / contrastive as if
as though
like
whereas
while
whilst
He used the stone as though / if it were a hammer.
She prefers to eat out while / whilst I prefer eating at home
I had eaten whereas the others had gone hungry

Both as if and as though are often followed by a subjunctive form.  There is a guide to this and other uses of the subjunctive on the site, linked below.
The conjunction like is often considered an informal version of as if and is not followed by the subjunctive.
The subordinators while and whilst are also temporal conjunctions.
proportional the ... the
more/less ... than
as ... so
The more they shouted the calmer he became.
She was more embarrassed than she ever remembered being.
As the evening wore on so they became noisier and more excited.
In the first example, the word the looks like the definite article but is, in fact an adverb.
In the second example, it is easily argued that the first element of the subordinator is simply a modifier.  That is so.

* The words that and as can act concessively in very formal and unusual expressions such as:
    He did not give things away, rich that he was
    Late as I was, I didn't miss most of the introduction
which is more often expressed with although as in:
    He didn't give things away although he was rich
    I didn't miss most of the introduction although I was late
In this case, the conjunctions are also unusual in not taking the initial position in the clause.

ball

Causal / Resultative subordination

There are a number of factors with this type of subordination which cause some difficulty.
Here are some notes to help:

  1. in case
    operates differently in AmE and BrE:
        She will take her laptop in case it's needed
    is differently understood.
    In British English, this means
        She will take her laptop and use it if she needs it
    In American English, this might mean:
        She will take her laptop only if there's a need for it
  2. whereby
    is unusual and almost always formal and often means something like with the aid of as in, e.g.:
        She left the door unlocked whereby the bird escaped
    it is probably only worth troubling advanced learners with this conjunction.
  3. as, since, seeing that and because
    all function as causal subordinators with the same syntax so we find:
        We stayed at home as it was raining
        We stayed at home because it was raining
        We stayed at home since it was raining
        We stayed at home seeing that it was raining

    are functionally synonymous.
    However, the usual ordering of the clauses is slightly different.
    1. as, since, seeing that
      all refer to the circumstance which caused the event (or non-event) so a more natural ordering would be:
          As it was raining we stayed at home
          Since it was raining we stayed at home
          Seeing that it was raining we stayed at home
    2. because
      on the other hand, emphasises the reason rather than the cause so the ordering naturally remains as:
          We stayed at home because it was raining
      not as
          Because it was raining we stayed at home
      which is possible but less natural.
  4. for
    in this sense, is a coordinator and can only be used between the two clauses.  We can allow:
        We stayed at home for it was raining
    but not
        *For it was raining we stayed at home
    and the use in coordination is formal and quite unusual.
  5. as and since
    can both function as temporal subordinators and since can also be a temporal preposition:
        She arrived just as I left
        He has lived here since he finished university
        He has lived here since his graduation
  6. so that
    functions as both a subordinator and a coordinator but with a different meaning:
    1. as a coordinator, not a subordinator, it is akin to so and refers to a result.  For example:
          The garden was covered in snow so that he could see the footprints clearly
      and In this sentence, so that can be replaced with a true coordinator such as and or so.
      Because it is a coordinator, it cannot shift position so we don't allow:
          *So that he could see the footprints clearly the garden was covered in snow
    2. When it is used as a subordinator its function is to refer to purpose rather than result to mean something like in order that, and it is subordinating in function so we can shift the clauses around as in, e.g.:
          He fixed it firmly in place so that it wouldn't move
          So that it wouldn't move he fixed it firmly in place
      It is possible that some ambiguity may arise.  For example, does:
          Someone stole my car so that I couldn't get to work
      mean that someone stole the car in order to prevent me getting to work or is the result of the theft the fact that I couldn't get to work?
  7. because
    can also be a source of ambiguity when it is used with a negative main clause as in, e.g.:
        She didn't come because John would be there
    which could mean either:
        The reason she didn't come was that John would be there
    or
        The reason she didn't come was not that John would be there (but arose from some other motivation)
    Intonation and sentence stress (on the subordinator) will disambiguate this is speech but only rephrasing can do so in the written form.
  8. lest and for fear that
    are both formal and quite rare:
        They covered the work with canvas lest it rain(ed)
        She took a sweater for fear that the weather would turn cold
    and are often used with a subjunctive form.
  9. Causal / Resultative clauses are normally finite (see below).
clock

Temporal subordination

He woke before the alarm went off  

There are rather too many subordinating temporal conjunctions in English and they cause a certain amount of difficulty for learners (and teachers) so they merit consideration here in a separate section.

Above, the following 18 items are listed as temporal subordinating conjunctions:
after, as, as soon as, before, hardly … when, immediately, no sooner … than, now (that), once, scarcely … when, since, till, until, when, whenever, whereupon, while, whilst
and many of them are synonymous in some respects but not in others.  Few languages have such a rich source of these sorts of subordinators so choosing the correct one to use and getting the syntax right is challenging.
Here are some notes to help:

  1. as, as soon as, when, while and whenever are not synonyms
    The conjunction when is quite versatile but the others are more restricted in their uses.
    We can allow, for example:
        She left when he arrived
        She was working in the garden when he was washing the car
        He was living in London when he died
        When I want to talk to him he's always too busy

    but if we try to replace the conjunction with the other common subordinators, this happens:
    1. as
          She left as he arrived
      carries a different sense.  The use with when implies shortly after he arrived but the use of as implies at exactly the same time.  In the sentence with when we might assume that his arrival was a reason for her leaving but we can make no such assumption when the subordination is achieved with as.
          She was working in the garden as he was washing the car

      is somewhat unusual but possible and carries more or less the same meaning although because the conjunction is also used causally might be interpreted as
          Because he was washong the car, mshe was working in the garden.
      Additionally,
          *He was living in London as he died
      is simply not possible because the sense of as is at that precise time and that is not carried by the progressive tense form in the sentence and.
          *As I want to talk to him he's always too busy
      is also malformed because the sense of as is confined to a single rather then repeated event or state.
    2. as soon as
      is an emphatic form of as and carries a little more strength.  It cannot, however, be used as a substitute except in the first sense so we allow:
          She left as soon as he arrived
      to carry the sense of immediacy.  However:
          *She was working in the garden as soon as he was washing the car
      and
          *He was living in London as soon as he died
      are both disallowed for the same reasons that the single form as is not allowed.
          ?As soon as I want to talk to him he's always too busy
      is only marginally acceptable and implies at the moment when I decide which is unusual.
    3. while
      can only be used to link progressive or background (continuous) states so if we produce:
          *She left while he arrived
      the sentence is malformed.
          She was working in the garden while he was washing the car
      is perfectly acceptable because both events are progressive and that is the usual use of this conjunction.
          *He was living in London while he died
      is another malformed sentence because the verb die is punctual in this sense and is not perceived as referring to a long-duration event (although it can).
          *While I want to talk to him he's always too busy
      is also malformed because although while can be used to refer to a background continual state, it cannot refer to the iterative (repeated) sense of whenever which is carried by when in this example.
    4. whenever
      refers to iterative events and cannot be used to refer to one-off or progressive events so:
          She left whenever he arrived
      can only refer to a habitual response to a repeated event.
          She was working in the garden whenever he was washing the car
      results in a similar and quite unusual sense of a repeated, long-duration event rather than a singled pair of progressive actions.
          *He was living in London whenever he died
      is clearly nonsensical because dying cannot be repeated
          Whenever I want to talk to him he's always too busy
      is the usual sense of the subordinator and refers to a repeated pair of events.
      Finally, whilst is a synonym of while and commonly misused when the simpler form while is stylistically preferable.  (The word is, in fact, an old genitive form of while and functionally redundant in English.)
  2. while and whilst
    also function as contrastive conjunctions and can imply concession as in, e.g.:
        While / Whilst he isn't rich, he has enough to live comfortably
  3. hardly .... when, no sooner ... than, scarcely ... when
    are synonymous in most cases but they share a characteristic of other negative adverbials in insisting on an alteration to word ordering making a question form with do, did, does or by inversion of auxiliary verb and main verb as in, e.g.:
        No sooner had he arrived than she left
        Hardly had he arrived when she left
        Scarcely did he arrive when she left

    and all suggest an almost simultaneous pair of events.
    The last example here is slightly unusual because these subordinators usually occur with past perfect tense forms.  The structure is:
        No sooner / Hardly / Scarcely + past perfect + past simple
    None of these can be used with long-duration or progressive events because by their nature they refer to two virtually simultaneous events.  So:
        *No sooner was she working in the garden when he was washing the car
    etc. are not allowed and we cannot allow:
        *Hardly was he living in London when he died
        *Scarcely do I want to talk to him than he's always busy
  4. before, after
    are straightforward and translate precisely into many languages, causing few conceptual and no structural issues.
  5. immediately, now that and once are not exactly synonymous
    The first implies at almost the same exact time (rather like as) but once implies shortly afterwards and because so, for example:
        She left immediately he arrived
    implies a very short time thereafter but
        She left once he arrived
    implies a longer time gap and possibly a causal connection.  For that reason, the past perfect form is often preferred, as in:
        She left once he had arrived
    The conjunction now (that) is frequently used to in present perfect constructions to embed the past event in the present and signal the causal nature of the two states as in, e.g.:
        Now (that) Mary has arrived, we can start.
  6. since
    occurs both as a preposition as in:
        He has lived here since the war
    and as a subordinating conjunction as in:
        He has lived here since the war finished
    The conjunction may also occur in a non-finite clause structure as in, e.g.:
        Since finishing university he has been unemployed
    and that is an unusual role for a subordinating conjunction.
    Few languages have a parallel structure like this.
  7. till and until
    are synonymous although the first is far less formal (and sometimes further reduced to til).  Both mean up to the time when.
  8. whereupon
    is quite an unusual conjunction which always occurs linked to the second, subordinated clause because, semantically, it strongly implies a causal connection as in:
        He arrived, whereupon she left

Not listed above are some common noun phrases which perform a subordinating grammatical function including, for example:
    (At) The moment he arrived she left
(compare as, as soon as)
    Every time I want to talk to him he's always busy
(compare whenever)

Temporal subordinators vary in whether they allow non-finite or reduced clause constructions and that is set out below in the restrictions section.

theme rheme

Clause ordering: theme and rheme

Because subordinators are linked to the clause (unlike coordinators which usually come between the clauses), the ordering of the clauses can be reversed and still produce a sensible sentence.  We can have therefore:
    Whereas most of the children arrived late, Mary was on time
or
    Mary was on time whereas most of the children arrived late
and
    Wherever I went, I encountered nothing but friendliness
or
    I encountered nothing but friendliness wherever I went
and so on.

However, in English, word ordering determines what the reader / hearer will understand as the theme of the sentence.  Above, the themes are highlighted in black.  What follows the theme is called the rheme and that, incidentally, frequently forms the theme of the next sentence, maintaining coherence and cohesion in a text.

When subordinate and main clauses are reversed, so are the associated themes and rhemes.  So, for example:
    Because she wanted to meet his mother, she travelled up to London
and
    She travelled up to London because she wanted to meet his mother
are not simply alternative ways of saying the same thing as the themes (in black) show.
Theme and rheme are identified by word order and word order is not selected at random.
Speakers and writers will select the word order to match what they perceive as the theme of the sentence.
Naturally, the first sentence would be followed by something about London such as:
    While she was there, she took the opportunity to visit the British Museum
and the second sentence would be more naturally followed by something about the mother such as:
    She was delighted to see her
If we follow the first sentence with something more appropriate to the second we get:
    Because she wanted to meet his mother she travelled up to London.  She was delighted to see her
in which we are left in a state of ambiguity regarding who was delighted to see whom.
If we follow the second sentence with the theme appropriate to the first, we get:
    She travelled up to London because she wanted to meet his mother.  While she was there, she took the opportunity to visit the British Museum
which is only marginally coherent.

The other indicator of what is perceived as the most important information is to note that pitch will rise and fall most obviously on London and mother respectively, signalling that this is the new information.

Reversing the clauses has a real and important communicative effect.

For more on theme-rheme structures, see the guide, linked below.

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alternatives

Alternative ways to subordinate

There are four major ways in which English can signal a subordination of one clause to another without using a conjunction (although conjunctions are by far the most frequent).

wh-words
Frequently, wh-words occur in pronoun and adverb relative clauses.  They function to split the main clause, inserting the relative clause into the sentence like this:
    The shop, where you bought the coat, has closed.
There is, however, a crucial difference because adverb relative clauses perform a coordinating, not subordinating function and can be removed to leave two well-formed independent clauses so we can rephrase:
    That was the moment when he realised the truth
as
    That was the moment.  He realised the truth.
which, although the sense is lost to some degree, results in two potentially independent clauses.
When, on the other hand, the relative pronoun is removed from a sentence the structure's subordinating function becomes apparent because removing it from, for example:
    He was the man who lent us the money
leaves nonsense.
The subordination occurs with both defining and non-defining relative pronoun clauses:
    The people who came to the party were genuinely friendly.
The relative pronoun that is used in a similar way:
    The dog that bit him belongs to the neighbours.
When omitting the relative pronoun is allowed (i.e., when it stands as the object in a defining clause, subordination still occurs
    The man we asked was very helpful.
There is a guide to relative pronoun clauses on this site linked in the list of related guides at the end.
that clauses
The word that is not in itself in any lists of subordinating conjunctions.  It is, however, an indicator of subordination and occurs, for example, in sentences such as:
    That he was drunk was obvious to everyone
where it functions as the subject of a copular verb
    I expect that she will be late
where it functions as the object of the verb
    The result is that we can't afford it
where it functions as the complement of a copular verb.
That clauses do a lot of other things in the language, too.
what clauses
The word what can also act as an indicator of subordination.  For example:
    She told me what she wanted
where it is the object of the verb
    What he did made the situation more difficult
where it is the subject of the verb
    The outcome is what we expected all along
where it functions as the complement of the copular verb.
Inversions
This is a fairly rare occurrence in English in conditional sentences but in formal writing may be encountered.  The usual items are had, were and the putative should:
    Had I known you were coming, I would have got in some beer.
    Were you to try a bit harder, I feel sure you'd understand.
    Should you find yourself in any trouble, call me at once.

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mirrors

Non-finite adverbial-clause subordination

Non-finite forms are those in which the verb is not conjugated to show person, tense or number.  For example:
    He came because I asked
contains two finite clauses, the second subordinated and both of which contain a conjugated verb showing tense (in English; in other languages the verb form might also show person and number).
However, in:
    Having been asked, he came
contains two clauses, again, but the first is non-finite because it does not show tense in the verb form in the conventional way.

This is a large category.  If you have followed the guide to clause structure, you'll know that independent clauses cannot be non-finite but that a non-finite clause is almost always a marker of subordination.  If the terms confuse you, there is a guide to finite and non-finite clauses on this site linked in the list of related guides at the end.  Here are two examples:
    I came (in order) to help (non-finite to-infinitive clause)
    Opening the door, he saw the fire had burnt out (non-finite -ing clause)
These sorts of subordination may be replaced by the use of a subordinator.
    I came so that I can help
    When he opened the door, he saw the fire had burnt out

Non-finite adverbial clauses generally function as

  1. adjuncts (being integral to the sentence), for example:
        John, having no work on, was happy to come and help
  2. disjuncts (showing the speaker / writer's attitude to what is being said), for example:
        Personally speaking, I have no objections
  3. conjuncts (linking two clauses or sentences), for example:
        It's going to be difficult to do within the budget.  That having been said, we may be able to manage

There are five ways in which non-finite adverbial clauses can be used to subordinate.  As is the case for subordinating conjunctions, they answer questions such as when?, where?, with what?, how?, what if? and so on.  When these clauses are used without a conjunction, they may be referred to as absolute clauses.

  1. The bare infinitive
    For example:
        Rather than do it himself, he called in a builder
        Sooner than have a problem later, she made sure it was well done
    These clause types are actually quite rare and usually signal exclusiveness.
    All such non-finite constructions can be rephrased using finite forms with subordinators:
        Because he didn't want to do it himself, he called in a builder
        She made sure it was well done so that she didn't have a problem later
  2. The to-infinitive
    For example:
        To see better, he stood on tiptoe
        Soon to be given a pay rise, she splashed out on a new car

    In some cases, the infinitive form is actually prepositional in nature because it is an abbreviated form of in order to and answers the question why?
    The connection is usually causal.
    All such non-finite constructions can be rephrased using finite forms with subordinators:
        So that he could see better, he stood on tiptoe
        Because she was soon to be given a pay rise, she splashed out on a new car.
  3. The -ing participle
    For example:
        Having no work, he slowly spent his savings
        Watching TV, being bored and not having anything better to do, I saw something about it on the news

    In almost all cases, the form implies a causal or temporal connection.
    All such non-finite constructions can be rephrased using finite forms with subordinators:
        He spent his savings because he had no work
        When I was watching TV because I was bored and didn't have anything better to do, I saw something interesting about it on the news
    Misuse of the -ing participle in non-finite clauses often results in what is called a dangling or unattached participle.  For example:
        Getting on the bus, John's wallet fell from his pocket
        Asking my students, they tell me they find non-finite clauses difficult to use

    are semantically and grammatically flawed because it was not the wallet that got on the bus or the students who did the asking.  To avoid this kind of error, the participle and the main clause verb need to have the same subject.  The use of a finite clause solves the issue:
        While he was getting on the bus ...
        When I have asked my students ...
    The rule of attachment to the same subject is often relaxed so we allow:
        Being Friday, the staff left early
        Being optimistic, Mary will be able to do the job
    (which could be ambiguous depending on whether the speaker or Mary is the optimist).
  4. The -ed participle
    (This is a slight misnomer in that irregular verb forms do not take -ed endings so the form is often called the -en participle.)
    For example:
        Tired and worn out, he went to bed
        Opened, the box revealed its secrets

    Again, in almost all cases, the form implies a causal or temporal connection.
    All such non-finite constructions can be rephrased using finite forms with subordinators:
        As he felt tired and was worn out, he went to bed
        As soon as it was opened, the box revealed its secrets
  5. Verbless clauses
    (This appears to be a contradiction if one assumes that all clauses contain verbs but can be analysed as ones in which the verb is omitted and understood.)
    For example:
        In sunshine or in rain, the garden was tended beautifully
    (= Whether there was sunshine or rain ...)
        Acceptable or not, the work must be paid for
    (= If it is acceptable or not ...)
    Some verbless clauses, known as supplementing clauses, refer to the whole of the preceding clause and omit all of it, including the verb.  They are usually afterthoughts or additions to a statement and are avoided in formal writing.  For example:
        I had finished the report – scarcely
    (= I finished the report but only scarcely finished it)
    Some verbless clauses, known as appended clauses, apply to part of the preceding clause only and are slightly more formal, being used in written and spoken forms.  For example:
        The child was tired, perhaps overtired
    (= The child was tired.  The child was perhaps overtired)

Non-finite clauses can also be used in the conventional way with subordinating conjunctions.  Here are some examples of all eight types of subordination in the table above:

Conditional
    When known, the cost should be published
(= If it is known, the cost should be published)
There is some ambiguity with a temporal connection here because it could mean
    As soon as the cost is known it should be published.
Concessive
    Although proven, the accusation was ignored by the court
(= Although it was proven, the accusation was ignored by the court)
Causal / Resultative
    Because of being tired, he left early
(= Because he was tired, he left early)
Temporal
    When digging in the garden, he found the coin
(= When he was digging in the garden he found the coin)
Exclusive
    When not including John, we'll be eight for dinner
(= If we don't include John, we'll be eight for dinner)
Spatial
    Wherever placed, it's going to be unsuitable
(= Wherever it is placed, it's going to be unsuitable)
Comparative / Contrastive
    As if stung, he jumped suddenly
    (=As if he had been stung, he jumped suddenly)
Proportional
    The more extreme, the more likely he was to hold the view
(= The more extreme a view was, the more likely he was to hold it)

The sorts of non-finite clauses used to express temporal or causal relationships can give rise to some ambiguity of meaning.  For example:
    Being in New York, she went to see him
could mean:
    While she was in New York, she went to see him
or
    Because she was in New York, she went to see him.

do not cross

Exclusions

It is not possible to use non-finite clauses with a range of conjunctions.
If these conjunctions are used with non-finite clauses, the result is unacceptable so we cannot allow those in the left-hand column.  We must rephrase the sentences to use finite clauses as in the right-hand column:

Faulty use with non-finite clauses Correct use with finite clauses
*As being ready I left the house As I was ready, I left the house
*Wherever putting it, it looked wrong Wherever I put it, it looked wrong
*Because arriving too early, I had to wait a long time Because I arrived too early, I had to wait a long time
*In order that fixing it firmly, I used long screws † In order that it was firmly fixed, I used long screws
*So that seeing his daughter he travelled to London So that he could see his daughter, he travelled to London
*As long as not breaking it, you can borrow the drill As long as you don't break it, you can borrow the drill
*The more shouting the less she will listen The more you shout, the less she will listen
*Seeing that broken, I'll buy a new one Seeing that it is broken, I'll buy a new one
*Now that finished, we can go home Now that we have finished, we can go home
*On condition that paid, you can leave at any time On condition that you have paid, you can leave at any time
*Supposing raining, what will you do? Supposing it rains, what will you do?
*As long as being here, you can come with us As long as you are here, you can come with us
† The prepositional phrase, in order to, is generally followed by a non-finite bare infinitive with the same kind of meaning.

Other subordinating conjunctions are more forgiving and allow both finite and non-finite clauses:

Use with non-finite clauses Use with finite clauses
While reading the newspaper, I noticed the mistake While I was reading the newspaper, I noticed the mistake
Since finishing college, he has worked from home Since he finished college, he has worked from home
He had few friends until joining our club He had few friends until he joined our club.
Although feeling very tired, she decided to go to the party Although she felt very tired, she decided to go to the party
If passed the law will make it illegal to buy those If it is passed the law will make it illegal to buy those
If visiting London, be sure to see The British Museum If you are visiting London be sure to see The British Museum
Unless performed, the play will be forgotten Unless it is performed, the play will be forgotten
Before re-opening, the pub was very scruffy Before it re-opened, the pub was very scruffy
Whether raining or not, I'm taking the dog out Whether it is raining or not, I'm taking the dog out
He kept his words simple as if speaking to a child He kept his words simple as if he was speaking to a child
Once finished, they could relax Once they had finished, they could relax
When speaking to her, he is always polite When he speaks to her, he is always polite
Till told, I had no idea Till I was told, I had no idea
† There are some who will not accept the use of until with a non-finite clause.
‡ Other conditional subordinators cannot be used with non-finite clauses (see above).

The restrictions on the use of non-finite clauses with some subordinators is not parallelled in many languages and a source of a good deal of error (see the first table for some examples).

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pegs

Subordinate clause position

Whether finite or non-finite, with true subordinating conjunctions or marginal ones, subordinate clause position is flexible.  The clause can be:

Initial
Because she wanted the job, she accepted less money
If you want to catch the train, go now
Watching the game, I noticed the referee's bias
Final or Terminal
She left because she was tired
You have to come now, whether ready or not
I'll come to see you when I get time
Mid or Medial
John, feeling miserable, decided to stay at home
The work, despite costing so much, was well done
You can, if you like, leave now

The medial position is both more formal and less common (and harder to understand, not only for learners).

weight

Weighting

If there are two subordinated clauses, the final one carries the most weight so, for example:
    She went home to bed when the film finished because she was tired
emphasises her tiredness, but:
    She went home to be because she was tired when the film finished
may imply that it was the film that made her tired or that she was tired in any case but either interpretation emphasises the end of the film.

ambiguous

Ambiguity

Ambiguity can, as we have just seen, be caused when there are two subordinate clauses because it is not always clear whether the subordination belongs to the main clause or to another subordinated clause.  For example:
    I expected he would be happy with the figures before the meeting started
can be interpreted either as:
    Before the meeting started, I expected he would be happy with the figures
or

    That he would be happy with the figures before the meeting started was what I expected
moving clauses around or rephrasing is usually the only way to avoid the ambiguity in written language but intonation and pausing play a significant role in speech.

right

Right ordering

There is a tendency in English to order subordinate clauses to the right of the main clause in the terminal position.  There is more on this is the general overview of subordination and coordination (first link below) but one important restriction should be noted here:
It is not possible to embed one subordinate clause inside another in the initial position without a conjunction so we allow, e.g.:
    She accepted less money because, having ambitions in the area, she wanted the job
and
    Because she wanted the job and had ambitions in the area she accepted less money
but not
    *Because, having ambitions in the area, she wanted the job she accepted less money
The usual ordering is either:

Subordinate clause 1 Main clause Subordinate clauses 2, 3, 4 etc.
As he felt ill John stayed at home where he did what work he could because it was urgent

or

Main clause Subordinate clause 1 Subordinate clauses 2, 3, 4 etc.
You should leave soon if you want to catch the train because the traffic is heavy in the evenings and you may be delayed

go

Pronoun reference

Subordination allows for pronoun referencing to be either cataphoric (referring forward) or anaphoric (referring back) and that distinguishes it from coordination which only allows anaphoric referencing.  We can allow, for example:
    Mary was tired and she stopped arguing
because the reference for the pronoun she has been stated, but we cannot allow:
    She was tired and Mary stopped arguing
unless she and Mary refer to different people.
However, with subordination we can allow both sorts of referencing so:
    Because she was tired, Mary stopped arguing
    Because Mary was tired, she stopped arguing

are both acceptable.
Equally, we can allow:
    John argued although he was tired
and
    Although he was tired, John argued.
In other words, in sentences with subordinated clauses, the assumption will always be that the pronoun reference and the noun refer to the same entity whichever way the referencing goes.

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pron

Pronunciation issues

Features of connected speech affect how subordinated clauses are pronounced in the normal way of things so rhythm and stressing are features which need to be taught (not just practised in a parroting way).
However, additionally, all conjunctions are function rather than content lexemes and subject to a good deal of weakening and reduction in rapid connected speech, in particular.

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Related guides
the word-class map for links to guides to the other major word classes
subordination and coordination for an overview of the area
coordination for the guide dedicated to this area
theme-rheme structures for more on how this works and some discussion of subordination
syntax: clauses and phrases for the index to allied areas
adverbials for more on the distinction between adjunct, disjunct and conjunct
conjunctions for more on the word class in general
so and such for a short guide to these two troublesome words
conditional and concessive clauses for more on two specific types of subordination
subjunctive for more on the other uses of the subjunctive in English
relative pronoun clauses for more on a particular type of subordination using pronoun forms rather than conjunction
relative adverb clauses for more on subordination using adverbs
finite and non-finite clauses for a guide to these two basic clause and verb types
ambiguity for a guide which considers how subordination and coordination can lead to ambiguity but sets it in a broader picture
lesson on subordination a lesson on subordination for higher-level learners
exercise on subordination a short exercise on subordination to test learners (and you)


Try a short test.


References:
Carter, R & McCarthy, M, 2006, Cambridge Grammar of English, Cambridge: Cambridge University Press
Quirk, R & Greenbaum, S, 1973, A University Grammar of English, 5th edition. London: Longman
Quirk, R, Greenbaum, S, Leech, G & Svartvik, J, 1985, A Comprehensive Grammar of the English Language, New York: Longman