What is the Comma Fault?
Basically, it is the serious punctuation error of joining two complete sentences with a comma. We all know that a sentence must end in a full stop (period, in US terminology), so it seems incredible that anyone would make this error, but it often happens when two sentences seem so closely related that they should be joined. [NOTE: this close relationship can be better represented with legitimate punctuation and I will deal with that in a moment].
What is a Complete Sentence?
A complete sentence has a finite verb and a subject. By convention, it starts with a capital letter and ends with a full stop/period. a sentence can consist of just two words, if they happen to be a subject and finite verb.
E.G. John wins.
John is the subject and 'wins' is a finite verb because it is limited by present tense and third person, so John wins is a complete sentence. [If that is gobbledygook to you and you would like a full explanation of what a finite verb is, just let me know ... email me or leave a message after the blog post].
Creating Longer Sentences
In practice, most of our sentences are much longer than two words.
E.g. John wins at Scrabble every time he plays, so no one wants to play against him.
OR
He buys one every Saturday night.
I chose this last sentence to illustrate that a sentence doesn't have to be clear to be a true complete sentence. In this case, we have no idea what 'one' happens to be, but we know John (the subject) buys (the finite verb) one every week. Thus, while the object of John's desire is unknown to us, the sentence is still a complete sentence.
What Generates the Desire to Make the Comma Fault?
What if that strange sentence above (He buys one every Saturday night) followed another that clarified its meaning... for example: 'Bill loves pepperoni pizza.' So, now we know that 'one' refers to a pizza.
The two sentences are so closely related that many new writers are inclined to join them with a comma.
Bill loves pepperoni pizza, he buys one every Saturday night.
That, sadly, is the error known as a comma fault. The first complete sentence does not end with the required full stop and the second complete sentence does not start with the required capital ... so it is wrong, wrong, wrong.
How to Fix the Comma Fault (1)
The simplest way to fix the comma fault is to introduce a conjunction (a joining word). Here, for example, we could write: Bill loves pepperoni pizza, so he buys one every Saturday night.
When we add that coordinating conjunction, the comma is then OK.
How to Fix the Comma Fault (2)
The second way to fix a comma fault is to replace that errant comma with the correct semicolon. A semicolon is meant to be used to join two complete (and related) sentences.
Bill loves pepperoni pizza; he buys one every Saturday night.
It started to rain; we put off our trip to the beach for a better day.
There is no excuse for speeding; everyone knows the law.
If you observe these sentences, you will see that both portions (before and after the semicolon) are stand-alone independent clauses ... for that, read mini-sentences. The semicolon is the perfect means to join them; the comma is completely wrong.
Why do I say the semicolon is used to join two complete and related sentences? The fact still remains there must be a sense that one part contributes to the other, or else a semicolon would seem strange. For example, the following use of the semicolon makes no sense.
The sky was a beautiful azure blue; when we arrived at the beach, we took off our shoes.
There is no clear relationship between the sky being a pretty blue and taking off our shoes, so the semicolon is wrong. However, as both are complete sentences, we must not use a comma either. A full stop is the only appropriate punctuation ... or else a complete re-working of the paragraph to make better sense and connectivity of ideas.