Run-Ons and Comma Splices

Run-ons and comma splices are related problems in writing. Both combine two independent clauses (or complete sentences) incorrectly; a run-on does so without adding a proper punctuation mark, and a comma splice does so without adding a coordinating conjunction.

Run-on sentences

Definition

A run-on sentence occurs when two complete independent clauses are mistakenly combined into one sentence without any punctuation. The sentence doesn't have to be long to be a run-on.

The ice cream melted in the sun and it ran down my hand.

Possible fixes

Here, two sentences are combined with a coordinating conjunction, but a comma is missing. Separate the two independent clauses using a semi-colon or a coordinating conjunction, or use a period if the two thoughts are unrelated.

The ice cream melted in the sun; it ran down my hand
(IC) semi-colon (IC)

The ice cream melted in the sun, and it ran down my hand.
(IC) comma + conjunction (IC)

comma splices

Definition

A comma splice occurs when two complete independent clauses are mistakenly combined into one sentence using only a comma.

Sharks are fish, whales are mammals.

Possible fixes

Here, two sentences are combined using only a comma. Like in a run-on sentence, you can fix the problem by separating the two independent clauses using a semi-colon or a coordinating conjunction, or using a period if the two thoughts are unrelated.

Sharks are fish; whales are mammals.
(IC) semi-colon (IC)

Sharks are fish, and whales are mammals.
(IC) comma + conjunction (IC)