An independent clause contains a subject and verb and is a complete thought – it is a simple sentence.
Example: The population of animals declined.
A dependent clause can’t stand alone as a complete sentence. It either lacks a subject, lacks a verb or is not a complete thought.
Example: When conditions worsened.
Independent + dependent clause: You can join a dependent clause to an independent clause to make a complex sentence.
Example: When conditions worsened, the population of animals declined.
Hint: See punctuation for when to use a comma with a dependent clause.
Independent + independent clause: You can join two independent clauses with either a comma and coordinating conjunction or with a semi-colon.
Example [comma and coordinating conjunction]: Linguistic analysis showed the early influence of Roman Latin on English, and this influence was later compounded by the arrival of the church.
Example [semi-colon]: Further analysis reveals the influence of Old Norse on English; the Viking longboats brought new words as well as new settlers to England.
Hint: See coordinating conjunctions and punctuation for more.