Subordinate clauses may be classified not only according to their use as parts of speech, but also, in quite a different way, in accordance with their various meanings. These distinctions in idea are of capital importance for the accurate and forcible expression of thought.
The variety of meanings which subordinate clauses may express is great, but most of these meanings come under the following heads.
(1) place or time
(8) indirect discourse
(9) indirect question
The general meaning of the clause is usually indicated by the word which introduces it.
Clauses of Place and Time
An adjective or an adverbial clause may express place or time.
1. The house where the robbery occurred is No. 14.
2. The bridge over which we rode is in ruins.
3. There is a point beyond which you cannot go.
4. The day when (or on which) I was to sail arrived at last.
5. The day before you came was rainy.
6. His terror while it thundered was pitiable.
1. Remain where I can see you.
2. That belongs where you found it.
3. Whithersoever I go, fear dogs my steps.
4. Whenever the bell rings, you must take down the receiver.
5. Esmond heard the chimes as he sat in his own chamber.
6. I have lived in Cairo since my father died.
Adjective clauses of place and time may be introduced by relative pronouns (see examples above).
Adjective and adverbial clauses of place and time may be introduced by relative adverbs. Thus….
Place : where, whence, whither, wherever, whithersoever, wherefrom, whereto, etc.
Time : when, whenever, while, as, before, after, until, since.
Clauses of time are sometimes shortened by the omission of the copula and its subject.
1. When [he was] rescued, he was almost dead.
2. Tom was attacked by cramp while swimming across the river.
An adverbial clause may express cause.
Causal clauses are introduced by the subordinate conjunctions because, since, as, inasmuch as, and sometimes that.
1. I came home because I was tired.
2. As the day was clear, we decided to climb the mountain.
3. Since you will not relent, you must take the consequences.
4. We were glad that the wreck was no worse.
5. Tom was delighted that his friend was safe.
SINCE is a preposition or an adverb when it denotes time; as is an adverb when it denotes time. Both since and as are conjunctions when they express cause.