Adverb Clauses:  Introduction

  1. When we were in Paris, we saw the Eiffel Tower.
  2. We saw the Eiffel Tower when we were in Paris.
When we were in Paris is an adverb clause.  It is a dependent clause.  It cannot stand alone as a sentence.  It must be connected to an independent clause.
Punctuation:  When an adverb clause comes before an independent clause, as in example a, a comma is used to separate the clauses.  When the adverb clause follows, as in example b, usually no comma is used.
  1. Because he was sleepy, he went to bed.
  2. He went to bed because he was sleepy.
Like when, because introduces an adverb clause.  Because he was sleepy is an adverb clause.
Summary List of Words Used to Introduce Adverb Clauses
(Subordinating Conjunctions)
TIME CAUSE & EFFECT OPPOSITION CONDITION
after
before
when
While
as
by the time (that)
since
until
as soon as
once
as/so long as
whenever
every time (that)
the first time (that)
the last time (that)
the next time (that)
because
since
now that
as
as/so long as
inasmuch as

so (that)
in order that
even though
although
though

whereas
while
if
unless
only if
whether or not
even if
providing (that)
Provided (that)
in case (that)
in the event (that)

Using Adverb Clauses to Show Time Relationships

after
  1. After she graduates, she will get a job.
  2. After she (had) graduated, she got a job.
A present tense, not a future tense is used in an adverb clause of time.  Notice in examples b and d regarding past tense.
before
  1. I will leave before he comes.
  2. I (had) left before he came.
when
  1. When I arrived, he was talking on the phone.
  2. When I got there, he had already left.
  3. When it began to rain, I stood under a tree.
  4. When I was in Paris, I visited the museums.
  5. When I see him tomorrow, I will ask him.
when = at that time

Notice the different time relationships expressed by the verb forms.
while
as
  1. While I was walking home, it began to rain.
  2. As I was walking home, it began to rain.
while, as = during that time
by the time
  1. By the time he arrived, we had already left.
  2. By the time he comes, we will already have left.
by the time = one event is completed before another event

Notice the use of the past perfect and future perfect in the main clause.

since
  1. I haven't seen him since he left this morning.
Since = from that time to the present
Notice that the present perfect tense is used in the main clause.
*Remember that depending on the context of the sentence since can also have the meaning of because.
until
till
  1. We stayed there until we finished our work.
  2. We stayed there till we finished our work.
until, till = to that time and then no longer (Till is used primarily in speaking rather than in writing.)
as soon as
once
  1. As soon as it stops raining, we will leave.
  2. Once it stops raining, we will leave.
as soon as, once = when one event happens, another event happens soon afterwards
as long as
so long as
  1. I will never speak to him again as long as I live.
  2. I will never speak to him so long as I live.
as long as, so long as = during all that time, from beginning to end
whenever
every time
  1. Whenever I see her, I say hello.
  2. Every time I see her, I say hello.
whenever = every time
the first time
the last time
the next time
  1. The first time I went to Paris, I visited the Eiffel Tower.
  2. I visited the Louvre the last time I went to Paris.
  3. The next time I go to Paris, I will visit Sacre Coeur.
Adverb clauses can be introduced by the following:

the first time (that)
the second time (that)
the third time (that)
the last time (that)
the next time (that)