Subordinating conjunctions

A conjunction that joins together clauses of unequal rank or importance is
called a subordinating conjunction. Read the following sentence:

• I told him that he should consult a doctor.

Here that joins together two clauses of unequal rank. I told him is the main clause, and that he should consult a doctor is a subordinate clause which is the object of the verb told in the main clause.
A subordinating conjunction connects a noun clause or an adverb clause to some other clause. Note that subordinating conjunctions are not used to connect adjective clauses.
Subordinating conjunctions introducing noun clauses
The most common subordinating conjunction used for introducing a noun clause is that; others are if, when, whether, why and how.

• I don’t know whether he will come.
• I think that he is trustworthy.
• I don’t care if he comes or not.

Subordinating conjunctions introducing adverb clauses
Adverb clause of time
Examples are: before, since, till, after etc.

• I returned home after he had gone.
• I have not seen him since we moved into this city.
• I will not forget that incident till I die.

Adverb clause of reason
Examples are: as, because, since etc.

• He may enter, as he is a friend.
• As he was not there, I left a message with his brother.
• He will get a promotion because he has proved his efficiency.

Adverb clause of purpose
Examples are: that, lest, in order that etc.

• We eat so that we may live.
• He held my hand, lest I should fall.
• Children should play games in order that their health may improve.

Adverb clause of result or consequence
Examples are: so…that

• He was so weak that he could hardly stand.
• She ate so much that she fell ill.

Adverb clause of condition
Examples are: if, unless, provided that

• I will go abroad if I get a good job.
• They won’t help you unless you tell them the truth.
• They will help you provided you tell them the truth.
• She spoke as if she knew everything.

Adverb clause of concession
Examples are: though and although

• He works hard though he is weak.
• She is always neatly dressed although she is poor.

Adverb clause of comparison
Example: than

• He is cleverer than I am.
• I like him better than her.

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