Expressing past time : using time clauses

(a) After I finished my work, I went to bed.
(b) I went to bed, after I finished my work.
After I finished my work= a time clause
I went to bed= a main clause
(a) and (b) have the same meaning.
A time clause can:
(1) come in front of a main clause, as in (a)
(2) follow a main clause, as in (b)
(c) I went to bed after I finished my work
(d) Before I went to bed, I finished my work
(e) I stayed up until I finished my work
(f) As soon as I finished my work, I went to bed
(g) The phone rang while I was watchinh TV
(h) When the phone rang, I was watching TV
These words inntroduce time clauses:
(After, Before, Until, As soon as, While, When) + subject and verb = a time clause
In (e): until ="to that time and then no longer"
In (f): as soon as="immediately after"
Punctuation: Put a comma at the end of a time clause when the time clause comes first in a sentence (comes in front of the main clause)
Time clause+comma+main clause
Main clause+no comma+time clause
(i) When the phone rang, I answered it
In a sentence with a time clause introduced by when, both the time clause verb and the main verb can be simple past. In this case, the action in the when- clause happened first. In (i). First: the phone rang. Then: I answered it.
(j) While I was doing my homework, my roommate was watching TV.
In (j): When two actions are in progress at the same time, the past progressive can be used in both parts of the sentence.