A comma signals a pause. To a beginning writer this pearl of wisdom is about as useful as a map is to a four years old with knowledge of neither orientation nor scale. To start with, there are different ways to signal a pause.
A Subject and Its Verb
The sentence Henry, he went to the cinema can certainly be uttered with a brief pause — hence the use of the comma — but in real life people can also break it up with other punctuation marks. For example:
- Henry… He went to the cinema. (to show ponderation, unwillingness to answer…)
- Henry! He went to the cinema. (to show surprise, scorn…)
- Henry? He went to the cinema. (to show perplexity, uncertainty…)
- Henry. He went to the cinema. (to show neutrality, detachment…)
However, all this variants, apart the one with ellipsis, become ungrammatical the moment we have the simpler sentence Henry went to the cinema.
This is so because a cardinal rule about comma usage is that a comma can never split a subject from its verb, no matter what.
In short, from a grammatical standpoint Henry, went to the cinema is always wrong. All the same, you might decide to break such a rule. But given that, as we have seen above, you have many alternative ways to signal a pause, I would say this is one of those few rules worth preserving.
Restrictive and Non-Restrictive Clauses
No comma between subject and verb, ever. All right. But then we come across phrases like Ellen, who was the new teacher, came from Milford.
This is potentially confusing. How is it possible? We can’t place a comma between subject and verb, but it’s fine if the commas are two?
Is this mess all about numbers… I mean the number of commas a sentence holds?
The short answer is: no, numbers don’t mean anything.
In fact, in this case the two commas act like parenthesis. They add information regarding the subject that isn’t essential to the meaning of the main clause.
In this case we can break down our sentence as follow:
Ellen, who was the new teacher, came from Milford –>
Ellen (who was the new teacher) came from Milford –>
Ellen came from Milford. She was the new teacher.
You can think of the two commas that set the boundaries for the non restrictive clause as sort of parenthesis. That’s why you can put them between the subject and verbs of the main clause, and you must always use them in tandem.
This process can be reiterated. For example: Ellen, who was the new teacher, and who had been hired only a week before, came from Milford.
As you can notice, in the above example the commas are only three. This is so because the two non restrictive clauses come one after the other.
Ellen, (1)who was the new teacher, (2) and who had been hired only a week before, came from Milford.
The same applies when you have even more non restrictive clauses in your sentence.
The first non restrictive clause requires two commas, the second and all the others only one each.
Ellen, (1) who was the new teacher, (2)who had been hired only a week before, (3)and had a slight lisp, came from Milford.
However pay attention to the following sentence:
Ellen, who was the new teacher, and who had been hired only a week before, came from Milford, a small city in Nebraska, a place I had never visited.
Here we have two more non restrictive clauses one right after the other. But they have to do with the adverbials of place (Milford) not with Ellen. So in this case too the first non restrictive clause requires two commas, and the the second only one. However, given it also ends the sentence, a period replaces the otherwise compulsory comma.
A Last Word
Non restrictive clauses can be useful. They are interesting resources of the language and can help writers to play with different styles. Just remember that when there are many of them, sentences tend to become quite difficult to understand.
As a result, make sure you know how to use them. And even then, unless you have a very good reason to do otherwise, or are a nobel prize winner for literature (and in this case I really don’t know why you would be reading this post…), use them sparingly. Not as I just did… Not always at least. Good writing!