Two complete sentences incorrectly joined by a comma make a run-on sentence.
Instances where commas should not be used include joining two complete sentences; complete sentences should be joined with semicolons. An example of incorrect use would be: "Instances where commas should not be used include joining two complete sentences, complete sentences should be joined with semicolons."
run-on sentence
contains two or more simple sentences joined by a comma and a coordinating conjunction or by a semicolon> and, but, nor, or for.
The coordinating conjunctions that can be used to combine two complete sentences with a comma are "for, and, nor, because, yet, so."
He won, he had the best score. This is an incorrect or comma splice sentence -- two distinct ideas joined incorrectly by a comma. Either rewrite as two sentences, or change the comma to a semicolon.
In formal writing a comma is not to be used two join two independent clauses. If comma is used between two sentences consisting of independent clauses it is known as comma splice. Two sentences formed by independent clauses should always be joined by a co-ordinate conjunction or a short punctuation mark such as semicolon if the sentences are closely related.
If it is possible to replace a comma in a given sentence with a period, and wind up with two sentences that are each complete and that make sense as sentences, then the comma that you replaced was being used to splice together two sentences. This is generally a bad idea.
A introductary prepositional phrase
A comma splice is the joining of two sentences by a comma without the use of a conjunction. For example:*Horace was a Roman poet, he died in 8 BC.Because these two utterances are complete sentences ("Horace was a Roman poet" and "He died in 8 BC"), they should not be joined with a comma. Here are three ways to improve the mechanics of the example:1. Use a semicolon instead of a comma--Horace was a Roman poet; he died in 8 BC.2. Write it as two sentences, separated by a period--Horace was a Roman poet. He died in 8 BC.3. Connect the two sentences by a conjunction, such as and--Horace was a Roman poet, and he died in 8 BC.
A comma splice is when a two complete sentences are separated by a comma, without a conjunction. This makes it gramatically incorrect. A run-on sentence continues on and on with no clear predicate.
When two sentences are written as one and seperated by a comma, they are called a run-on or fused sentence.