CoMpOuNd SeNtEnCeS

* A compound sentence contains two independent clauses joined by a coordinator.
* The coordinators are as follows: for, and, nor, but, or, yet, so.
* Except for very short sentences, coordinators are always preceded by a comma
 I tried to speak Spanish, and my friend tried to speak
Alejandro played football, so Maria went shopping. 

The above three sentences are compound sentences.  Each sentence contains two independent clauses, and they are joined by a coordinator with a comma preceding it.

Another Examples:

• "It was a bright cold day in April, and the clocks were striking thirteen."
  (George Orwell, Nineteen Eighty-Four, 1949)



• "The drought had lasted now for ten million years, and the reign of the terrible lizards had long since ended."
  (Arthur C. Clarke, 2001: A Space Odyssey, 1968)  
• "Feasts must be solemn and rare, or else they cease to be feasts."
  (Aldous Huxley)