Combining a Subordinate and a Main Clause

Combining clauses is what sentence building is all about. Joining a subordinate clause with a main clause requires only a comma:

✓ Because it was a sunny day, she decided to walk to the park.

(subordinate)                           (main)

Combining Two Main Clauses

The tricky part comes when two main clauses are joined together. Punctuation options include:

✓ A period: It was a sunny day. She decided to walk to the park.

✓ A semi-colon: It was a sunny day; she decided to walk to the park.

✓ A comma with a linking word (coordinating conjunction): It was a sunny day, so she decided walk to the park.

Other coordinating conjunctions are and, but, yet, or, nor and for.

✘ Comma splices: Do not use a comma to join two main clauses in a sentence: e.g., It was a sunny day, she decided walk to the park. A comma is too weak a form of punctuation, and the resulting error is called a comma splice.

✘ Run-on sentence: Joining two main clauses with no punctuation is called a run-on sentence.

Both are considered to be major sentence errors.

A special case is when two main clauses are combined, and the second one begins with however (or other conjunctive adverbs like therefore, thus or nevertheless). A semi-colon must be used; a comma is too weak, and will create a comma splice:

✓ It was raining; however, she decided to walk to the park.