As a child, you may have recited the catchy jingle, "Conjunction, conjunction, what is my function?" In grammar school and beyond, you learned that conjunctions are connectors -- words that join other words, phrases and sentences. Conjunctions can have different purposes, including joining similar ideas, joining contrasting ideas and joining alternative ideas.
Remember that coordinating conjunctions include "for," "and," "but," "so," "or," "nor" and "yet." To decide if you need to use a coordinating conjunction, determine the purpose of the sentence. For example, use "and" if you want to join two similar ideas. For example, you might write, "They went to the beach and then to the park."
Use "but" if you want to join two contrasting ideas. For example, you might write, "He is a sloppy dresser, but she is a neat dresser."
Use "so" if you want a coordinating conjunction to show that the second idea is the result of the first one. For example, consider "He was late for school, so he went to get a tardy note from the office."
Select "or" for a coordinating conjunction if you want to join two alternative ideas. For example, you might write, "I want to wear my green dress or my black dress."
Understand the comma usage when using conjunctions. If you are using a coordinating conjunction to separate two main clauses, you must use a comma before the coordinating conjunction. For example, you would write, "Ruby got out of bed, and she went downstairs to talk to her mother." The comma here goes before the conjunction "and."
If you have only one main clause and a subordinate clause, do not use a comma before the conjunction. Recall that a subordinate clause is not a complete sentence. For example, you would write, "Ruby got out of bed and went downstairs to talk to her mother." The subordinate clause is "went downstairs to talk to her mother."
Use subordinating conjunctions to introduce dependent clauses. Subordinating conjunctions, like coordinating conjunctions, are connectors. But subordinating conjunctions join two thoughts. Some subordinating conjunctions include "before," "after," "though," "although," "however" and "when." For example, consider, "Although he said he did not steal the cookies, there were cookie crumbs around his mouth." Here "Although he said he did not steal the cookies" is the dependent clause.
Use correlative conjunctions to link equivalent items in pairs. Such conjunctions might include phrases such as "both ... and," "either ... or," "neither ... nor" or "whether ... or." For example, you might write, "Johnny couldn't make up his mind whether to go to the park or to go to the zoo."