Subordinating conjunctions generally join a subordinate or dependent clause to a principal clause (a), or adverbial modifiers to the predicate in a simple sentence (b), or sometimes they join homogeneous parts (c).

When he was eight, he got work in another mill. (London)

He shook his head a bit as if in wonder that he had permitted himself to be caught in such crosscurrents. (Wilson)

My look or something else must have struck her as offensive, for she spoke with extreme, though suppressed irritation. (Ch. Bronte)

Subordinating conjunctions may introduce subject clauses, object clauses, predicative clauses, adverbial clauses, and attributive clauses.¹

Many of the subordinating conjunctions introduce different kinds of clauses. For instance, that may introduce subject clauses, predicative clauses, object clauses, adverbial clauses of purpose and of result.

That Ruth had little faith in his power as a writer did not alter her nor diminish her in Martin’s eyes. (London) (SUBJECT CLAUSE)

What I mean is that you’re the first man I ever met who’s willing to admit out loud to a woman that he thinks she’s better than he is. (Wilson) (PREDICATIVE CLAUSE)

He looked to the south and knew that somewhere beyond those blue hills lay the Great Bear Lake. (London) (OBJECT CLAUSE)

He walked into the Green Park that he might cross to Victoria Station and take the Underground into the City. (Galsworthy) (ADVERBIAL CLAUSE OF PURPOSE)

He bailed wildly at first, splashing himself and flinging the water so short a distance that it ran back into the pool. (London) (ADVERBIAL CLAUSE OF RESULT)

The conjunction if introduces object clauses and adverbial clauses of condition:

He was anxious to see if she had relapsed since the previous evening. (Dickens) (OBJECT CLAUSE)

If the man ran, he would run after him; but the man did not run. (London) (ADVERBIAL CLAUSE OF CONDITION)

The conjunction as introduces adverbial clauses of time, of cause, and of comparison:

These were the thoughts of the man as he strove onward. (London)(ADVERBIAL CLAUSE OF TIME)

As Jacob has made me captain, I must call the roll. (Dodge) (ADVERBIAL CLAUSE OF CAUSE)

That day had decreased the distance between him and the ship by three miles; the next day by two — for he was crawling now as Bill had crawled. (London) (ADVERBIAL CLAUSE OF COMPARISON)

The conjunction while may express both coordination and subordination. It may be a coordinating adversative conjunction or a subordinating conjunction of time.

Older men probably resented him while others of his own generation could feel so inadequate when comparing their talent to his… (Wilson)(COORDINATING CONJUNCTION)

While skating along at full speed, they heard the cars from Amsterdam coming close behind them. (Dodge) (SUBORDINATING CONJUNCTION)

Subordinating conjunctions may also be used in simple sentences. They join adverbial modifiers to the predicate of the sentence. Conjunctions of comparison, such as as if, as though are frequently used in simple sentences.

He scowled at first; then, as if recollecting something, he said… (Ch. Bronte)

He seemed faint and dizzy and put out his free hand while he reeled, as though seeking support against the air. (London)

The subordinating conjunctions though and if are also used in simple sentences:

Though alone, he was not lost. (London)

Next, he sheered to the left, to escape the foot of the bed; but this sheer, if too generous, brought him against the corner of the table. (London)

Subordinating conjunctions of time are rarely used in simple sentences. In that case they are mostly used with participles:

That she was one of those women — not too common in the Anglo-Saxon race — born to be loved and to love, who when not loving are not living, had certainly never even occurred to him. (Galsworthy)

Only rarely does a subordinating conjunction pin homogeneous member:

He was gay though tired.