Compound Sentences 

Compound sentences & coordinating conjunctions  

Key Terms 

  • Compound sentence 
  • Coordinating conjunction (SOY BAN): 
    • so 
    • or 
    • yet 
    • but 
    • and 
    • nor 

The easiest way to lengthen your sentences is to write compound sentences. Compound sentences are formed by joining two (or more) simple sentences by using a coordinating conjunction.  

You can remember these coordinating conjunctions by the acronym SOY BAN. 

Note: Many texts list “for” as a coordinating conjunction but it has become archaic, i.e., old-fashioned and hardly ever used. If you do see “for” being used as a conjunction, it means “because.” 

Formula: Independent clause + , + coordinating conjunction + independent clause 

Note about comma use: In general, use a comma BEFORE the coordinating conjunction. However, if both independent clauses are short, many authors will not use a comma. That being said, most teachers expect the comma, so it's safer to use one in a school setting. In the examples below, I've used a comma in some and no comma in the others. Read them out loud: do you find that a pause is necessary before the conjunction? If so, use a comma.

  • I prepared the ingredients early so I can cook as soon as I get home. 
  • We can eat out, or we can cook at home. 
  • I followed the instructions, yet it doesn’t taste right. 
  • I love pizza, but I shouldn’t eat too much. 
  • I cooked the soup and I baked the bread. 
  • I couldn’t find all the spices, nor could I get the fresh herbs.* 

*In compound sentences joined using nor, the second sentence inverts the subject and auxiliary. See below.

Compound sentences with “nor” 

In compound sentences joined using nor, the second sentence inverts the subject and auxiliary: 

1) I couldn’t find all the spices. I couldn’t get the fresh herbs. 

  • I couldn’t > nor could I 

I couldn’t find all the spices, nor could I get the fresh herbs. 


2) She wasn’t available on Monday. She’s not available today. 

  • She’s not > nor is she 

She wasn’t available on Monday, nor is she available today. 

"Then" is not a coordinating conjunction 

Then is NOT a coordinating conjunction. Using then as a coordinating conjunction results in a run-on sentence (ROS). The simple solution is to use "and then" in the middle of a sentence.  

INCORRECT Yesterday, I went to school then I went to the park. 

CORRECT Yesterday, I went to school, and then I went to the park. 

Can you start a sentence with a coordinating conjunction? 

Yes, you can. There is no rule against starting a sentence with a coordinating conjunction. However, don’t do it more than once or twice per page, or once in a short response. Due to the brevity of coordinating conjunctions – they’re all 2 and 3 letter words – their effect is abrupt and thus noticeable: starting too many sentences with coordinating conjunctions gives your writing a breathless feeling. So use them sparingly (like this sentence).