Subordinate conjunctions precede a subordinate clause, or one that cannot stand alone as a sentence. For a subordinate clause to make sense, it must rely on the main or subordinate clause, one that can stand alone as a sentence. While a subordinate clause can precede or follow the main clause, subordinate conjunctions introduce the subordinate clause. These conjunctions serve two purposes: to transition from one idea to the other within the same sentence and to place the emphasis of the sentence as a whole on the main clause.
There are many subordinate conjunctions that also function as prepositions. An easy way to remember the difference is that the word is a subordinate conjunction whenever it introduces a subordinate clause. If there is no subordinate clause, it is likely part of a prepositional phrase. The list of subordinate conjunctions includes (but is not limited to) the following conjunctions:
In most cases, the punctuation of a sentence is dictated by where the subordinate conjunction is placed. Remember that these always start a subordinate clause. If that clause appears before the main clause, a comma almost always follows it. If the subordinate clause (that starts with the subordinate conjunction) appears at the end of the sentence, a comma is rarely used. Consider the following examples:
Example 1: While the snow just kept coming down, it was not accumulating as quickly as you would think.
“While” is the subordinate conjunction that introduces the subordinate clause, and because it appears at the beginning of the complete sentence, it is separated from the main clause with a comma.
Example 2: It is difficult to decide on the right brand of computer whether you are buying a PC or a laptop.
“Whether” is the subordinate conjunction that introduces the subordinate clause, and since it is located at the end of the sentence, no comma is necessary to separate it from the main clause.
One of a subordinate conjunction’s purposes is to provide a transition between the two ideas contained within a complex sentence (one with both a main idea and a subordinate one). This transition is one that shows a relationship of adverb, noun or adjective subordinate clauses to the main clause. The transitions show a relationship of cause and effect, condition, contrast, place or time. Consider the following examples:
Example 3: Dawn made an appointment with her doctor when she was having post-surgery complications.
“When she was having post-surgery complications” is a subordinate clause that shows a relationship of time, or when Dawn made an appointment. “When” is the subordinate conjunction that connects the two ideas.
Example 4: Although Nathan was late for the party, he still had a great time.
“Although Nathan was late for the party” is a subordinate clause that shows a relationship of comparison or concession, or of Nathan arriving late for the party. “Although” is the subordinate conjunction that connects the two ideas.
The other purpose of subordinate conjunctions is to clue your readers in to which clauses are of more importance, even if they do not realize this is happening. The least important clause is contained within a subordinate clause and started with the subordinate conjunction. The main clause is made more important simply by the reduction of importance created through the use of the subordinate conjunction.
Reconsider the third and fourth examples in the preceding section. In example 3, making the appointment is more important than the fact that Dawn is having complications. In example 4, having a great time takes precedence over the fact that Nathan was late.