As you probably know, a conjunction connects words, clauses, phrases, and sentences. However, not all conjunctions are created equal, or more precisely, not all grammatical structures that conjunctions join are equal. The two main classes of conjunctions are coordinate and subordinate. The following will explain the difference between the two.
When most people think of conjunctions, they are usually thinking of the coordinating variety. The most common ones include and, but, or, and so. Coordinating conjunctions join words or groups of words that are equal in rank grammatically. For instance, in the following sentence the two nouns are separated with a coordinating conjunction.
Kristy served tea and cake.
However, as mentioned above they can also join entire phrases and sentences as in the following examples.
Andrew picked up the ball and tossed it to his older brother.
Jen enjoys a brisk jog in the park, but Linda prefers a quiet walk in the woods.
In these sentences, the conjunctions either join two predicates or two independent clauses. Keep in mind that when you use a conjunction to join two independent clauses, insert a comma between the first clause and the conjunction.
Subordinating conjunctions, on the other hand, connect grammatical structures (usually clauses) of unequal rank. A subordinating conjunction introduces a clause that is dependent on the main clause. The dependent clause can be introduced preceding the main clause in an introductory role, or it may follow the main clause to add meaning to the sentence. Some common subordinating conjunctions include although, as, before, until, when, and while. You can find a more complete list on the English Plus website.
As with coordinating conjunctions, the subordinate counterparts have a few punctuation rules to keep in mind. For example, when introducing a clause that precedes the main clause, insert a comma between the final word of the introductory clause and the first word of the main clause.
Before the girl returned home, she walked to the park with her friends.
However, if the subordinating conjunction follows the main clause, a comma is not necessary.
Shane remained at the library until his daughter called to ask for a ride home.
In this case, adding a comma was unnecessary because the subordinate clause was crucial to the meaning of the sentence.
Conjunctions aid writers in creating complex, meaningful sentences. Don’t forget to punctuate them correctly so you’re reader will understand your sentences.