Relative adverb clauses

relative adverbs

Relative adverbs are often considered quite simple structures in English but, because of the differences between languages and their stylistic complications, they are quite difficult to learn to use for many learners, especially those whose first languages differ from English in the use of relative adverbs (i.e., most of them).
What follows assumes you have followed a guide to relative clauses and/or are familiar with their structure.
The difference here is that relative adverbs modify the verb whereas relative pronouns refer to the noun (or whatever part of the sentence is performing a noun's grammatical function).
The difference can be exemplified by considering what it is that the speaker wants to highlight:

This is the house he bought
in which the pronoun which is referenced to the noun phrase the house because it is the most important element and the object.
We can re-phrase this as:
He bought this house (Subject – Verb – Object)
This is the house where he lived
in which the adverb where modifies the verb phrase lived because the location is what we need to highlight.
We can rephrase that as:
He lived here (Subject – Verb – Adverbial)

That, of course is one way in which adverbs and pronouns differ / how adverbs and pronouns differ.
Structurally, however, there are close parallels between adverbial relative clauses and pronoun relative clause because they both have the structure of
Noun phrase + Adverb / Pronoun + Verb phrase.

What are relative adverbs?

Simply put, they are adverbials. They are, in fact, adjuncts.
(If the term adjunct is unfamiliar to you, you need not worry about it now. It refers to the fact that the adverbial is integral to the sentence and not being used to connect two sentences or refer to the speaker's perception. There is a guide to this kind of analysis on the site.)

They act as adjuncts in four ways:

Place: This is the restaurant where we met.
We met here
Time: That was the moment when she decided to give up.
She decided to give up then
Reason: That was the reason why he got angry.
He got angry because of that
Manner: This was how he arrived at the figure.
He arrived at the figure thus

Style issues

Tautology: are relative adverbs unnecessary?

There are those who consider the use of relative adverbs unnecessary, superfluous, redundant and tautologous. So:

Adverb	Instead of ...	... some prefer an adverbial wh-phrase...	or a simple Subject + Verb + Adverbial structure
where	That is the hotel where he stayed	That is where he stayed	He stayed in that hotel
when	The was the time when she left	That is when he left	She left then
why	That is the reason why she hurt herself	That is why she hurt herself	She hurt herself because of that
how	No form possible	This is how it was done	It was done this way

This is certainly an arguable point of view when the noun (technically the antecedent noun) is a generalised word such as time, reason, place, location, phase, period, moment, building, house etc. Because the adverbial refers to a place, a time or a reason, it does seem unnecessary and many think it poor style, to insert the noun at all. In fact, as we shall see, the adverb how does not allow an antecedent noun at all.

Speakers do, however, have reasons for choices and there is a cline between wholly generalised nouns (such as place, time, period) to very specific ones (such as corner of the room, hour, exact second) with lots of more-or-less general terms in between (such as house, building, year, month etc.). There is, then, a stylistically acceptable range and individual users of the language will draw the lines where they will. You decide which you prefer in this list:

That was (the moment) when I decided.
This is (the building) where he died.
Here is (the room) where he wrote Bleak House.
That is (the day) when he was born.
That was (the year) when America became independent.
This is (the time) when we should stop.

And so on. The rule, such as it is, is:

If the speaker wishes, for whatever reason, to emphasise the nature of the antecedent noun, then it will be included in a relative clause.

Formality

Generally, the use of relative adverbs is considered less formal than the use of an adverbial prepositional phrase. It is easy enough for you to identify the formal and informal versions of the following. So click on the table when you have.

formal vs informal

The issue here for learners is that if they use the formal versions, they need to select the appropriate preposition and avoid errors like:

*That is the year on which he discovered it.
*This is the room at which they spoke.
*That was the day in which she arrived.

Using adverbial relative clauses avoids the need for the prepositions altogether because those three examples can be re-phrased as:

That is when he discovered it.
This is the room where they spoke.
That was when she arrived.

Form issues

Why

The use of why as a relative adverb is often considered plain wrong, whatever the circumstances.
Why should that be? Click here when you have the answer.

Virtually only the word reason can be the antecedent noun. We can have:
That was the reason why he came.
However, we can't have other words (even those which are close synonyms).
    *That was the purpose why he said it.
    *That was the ground why she complained.
    *That was the object why he went there.
    *This was the motive why she did it.
As this is the case, it seems actually unnecessary to teach why as a relative adverb at all because the antecedent reason can always be left out.
This leaves us teaching only the simple structure of why followed by a clause.

How

This word can operate as a wh- adjunct in expressions like:
    he told me how to do it
    she did it just how she wanted
etc. but it cannot function with an antecedent noun. It is not possible in English to have, therefore:
    *This is the manner how she did it.
    *This is the way how he told me.
It is possible to use it without the antecedent noun as in, e.g.,
    This is how she did it.
    This is how he told me to do it
There is an argument, therefore, that how is not a relative adverb at all.

Be aware that other languages are much more forgiving and how is commonly used with antecedent nouns. That is the root of many errors.

Defining vs. non-defining clauses

Both where and when as relative adverbs can be used in defining (restrictive) clauses or in non-defining (non-restrictive) clauses so the following are all possible but subtly altered in meaning.

either ...	... or ...	... but ...
The office, where he spends most of his time, is upstairs	The office where he spends most of his time is upstairs	The first gives us extra, supplementary information and the second defines the office.
That January day, on which she arrived, was foggy and cold	That January day on which she arrived was foggy and cold	The first gives us extra, supplementary information and the second defines the day in terms of her arrival.
That January day, when she arrived, was foggy and cold	That January day when she arrived was foggy and cold

The adverb why cannot be used in non-defining (non-restrictive) clauses. It always occurs, if we allow it at all, in defining (restrictive) clauses. We can, perhaps, have:
The reasons why he wanted the money are unclear.
but
*The reasons, why he wanted the money, are unclear.
is unacceptable.

The -ever series

For emphasis, the -ever suffix can be used. For example:
    I don't know why ever he did that!
    Do it however you like
    The office, wherever it is, is probably closed
Incidentally, why + ever is always written as two words.

Free relative clauses

These belong neither here nor in the guide to relative pronoun clauses. They are included here for simplicity because they share some characteristics with relative adverb clauses.

The reason these are called free relative clauses is that they do not refer to an already specified noun or noun phrase but contain within themselves the antecedent for the relative pronoun.
Here's an example of how they work with a little analysis:
    I don't know where he went
    What I need is a new hammer
    Why he came is a mystery
    How you do this is difficult for me to imagine
    Say what you like, he's been a great help to us
    Whoever said that is not telling you the truth
and so on.
All of these can be re-phrased using a relative pronoun or adverb clause as in:
    I don't know to which place he went
    It is a new hammer which I need
    It is a mystery why he came
    It is difficult to see how you do this
    Whatever you say, he has been a great help to us
    The person who told you that is not telling the truth.
etc.

Analysing these as free or, in some analyses, headless relative clauses is actually not too helpful.
What they really are, in most cases, is nominalised clauses, i.e., clauses performing the function of nouns, either as subjects or objects of verbs. For example,
The first example can be re-phrased with a simple noun phrase as:
    I don't know his location now
and we can nominalise the wh-phrase or clause as the subject or object of the verb:
    Where he is now is a mystery (subject)
    What he wants is a new car (object)
All these share the characteristics of nominalised clauses, to which, naturally, there is a guide on this site linked in the list of related guides at the end.
They can also be, rather more usefully, analysed as cleft sentences. See the guide linked in the list of related guides at the end, for more.

There are, in some analyses, two sorts of free relative clauses and we should consider them here:

Definite free relatives are introduced by what, where, and when. For example:
    He eats what he likes
    She went when she had heard enough
    I shall sleep where I can
Indefinite free relatives are introduced by who(m)ever, whichever, whatever, wherever, and whenever. For example:
    I can help with whatever you need
    Who(m) ever you ask will know where I live
    Whichever you choose will be OK
    Wherever you go you will see him
    Whenever he arrives, he'll be welcome

All these can, of course, and probably should, be analysed as nominalised clauses functioning grammatically as the object or subject of the verb or simply as adverbial phrases. In some cases, the issue is to do with subordination so the whole area of so-called free relative clauses is fraught with peril and, most probably, better left well alone.

Other languages and teaching the area

This is an area which needs handling with some care.

Many languages deploy similar constructions which sometimes makes comprehension of the function of relative adverbs straightforward (Italian, for example, operates very similarly to English). However, the restrictions above concerning what is possible and what is not, what is stylistically informal and what is not will not be readily understood because languages vary quite dramatically in this respect.

Grammatically, too, languages vary a good deal in this area with no one-to-one overlap between structures across languages. Some, for example, will use a different relative adverb in the past and in the present. Others will have words which function as relative adverbs but not as relative pronouns and vice versa.
Other languages, French and Romanian for example, use the same adverb for time and place.
Many languages, such as Spanish, Dutch, Czech, Russian, Swedish and other Scandinavian languages, German and Greek, abjure the use of why as a relative adverb, preferring a phrase translatable as for that or therefore. This expression differs from the form of why used in questions. So, instead of:
    This is why he came
the expression will be translatable as something
    Therefore he came
or
    For that he came
Some languages, such as Greek, do not have separate adverbs for all the functions and will form the clause with a relative pronoun instead, translatable as something like:
    That was the moment which he decided.
Many languages, such as Japanese and Korean do not use relative adverbs (or pronouns) at all, preferring to directly modify the verb rather than constructing subordinate clauses.

Production rather than comprehension should, therefore, be the focus because the forms are simple enough to understand (usually) but not at all intuitive to produce for speakers of many languages.

Form

Primarily, the issues to make sure of are:

The restrictions on the use of why
As we saw above, why can always be used without the antecedent noun (because only reason(s)) is the possible choice. That's a reason not to bother people with it and confine ourselves to teaching
That's why he came
This is why I'm asking
etc.
The fact that why cannot be used in non-defining clauses rarely causes problems.
The severe restrictions on the use of how in English are not paralleled in many languages so it is worth devoting a teaching sequence to its use in English or errors such as
*that's the way how I did it
*it is the right method how we do it
will occur frequently.
When they do occur, the sensible approach is to tackle the error immediately.

Style

is more important, arguably.

If the presentation of the area does not include a clear and explicit focus on style, then error will occur. In other languages, the distinctions are nothing like parallel. In German, for example, the use of prepositional phrases such as in which (in dem, for example) is standard and not considered particularly formal so speakers of Germanic languages can sound stilted when they use them, saying, for example:
    This is the classroom in which we meet
when a native speaker would probably prefer:
    This is the classroom where we meet
or just
    This is where we meet
Even in German, the alternative use of a relative adverb does occur, incidentally.

Leaving out generalised antecedent nouns can be handled by a compare-and-contrast, awareness-raising approach using, e.g.,

That was when he lost his temper vs. That was the exact time when he lost his temper.
This is where we eat vs. This is (the restaurant) where we eat vs. This is the Chinese restaurant where we eat.

Getting learners to notice the emphasis the speaker wants to put on the noun is an important first step to production.
Then you can go on to getting them to say something true about their own lives using both specific and more generalised nouns appropriately. As in, e.g.:
    the exact time when I was born vs. when I was born
    the village where I was born vs. where I was born
    the reason why I am learning English vs. the exact purpose for which I am learning English
etc.

Summary

Here's a brief cut-out-and-keep summary of the area:

summary

Related guides
adverbials	for more about adjuncts, conjuncts and disjuncts
relative pronoun clauses	for more on relative clauses using pronouns rather than adverbs
wh- questions	for an area allied to the use of relative adverbs
subordination	for more on other ways to make ideas depend on others
nominalised clauses	for more on an alternative way of seeing free relative clauses
cleft sentences	for a consideration of how to analyse some free relative clauses