Run-on sentences occur when a sentence with multiple independent clauses is improperly punctuated.

For example: I had a job interview that morning so I wore my best suit.

Both I had a job interview and I wore my best suit are independent clauses. You can’t just stick a coordinating conjunction between them to make a sentence.

Here are the two rules for punctuating multiple independent clauses in a sentence:

  1. Independent clauses may be joined with a comma and a coordinating conjunction. You can correct the problem by adding a comma, like this: I had a job interview that morning, so I wore my best suit.
  2. Independent clauses may be joined by a semicolon. The sentence can look like this: I had a job interview that morning; I wore my best suit.

You can also change one of the independent clauses to a dependent clause, like this: Because I had a job interview that morning, I wore my best suit. If you do that, remember to separate the clauses with a comma when the dependent clause precedes the independent one.